This study examines the utility of moving beyond a simple “on-off” dichotomous view of contiguous land borders. For each of the 301 contiguous land borders between states in the international system, measures of ease of interaction, salience, and overall border vitalness have been developed using Geographical Information Systems technology. These variables are used to test two major extant lines of thought in the international relations literature as well as an alternative proposed here, regarding the expected effect of the “nature” of borders on interstate behavior. We conclude not only that the “nature” of contiguous borders matters (and, thus, that analysts should move beyond looking at borders as simply existing or not), but also that the relationship between each of the three border measures and the likelihood of conflict is curvilinear concave.

This research project has been supported by grants from the University of South Carolina (Research & Productive Scholarship Award #13570-E120), and the National Science Foundation (SBR-9731056). Questions regarding the availability of the dataset should be directed to Harvey Starr.

Paper prepared for the Annual Meeting of the American Political Science Association, August 30- September 2, 2001, San Francisco.

The location of states, their proximity to one another, and especially whether or not they share "borders," emerges time and again as key variables in studies of international conflict phenomena: from major power general war, to the diffusion of international conflict, to the analysis of peace between pairs of democracies. From Boulding's (1962) ideas of "behavior space," "loss-of-strength gradient" and "critical boundary" to the simple but profound concern of geographers that humans interact most with those to whom they are closest, there are powerful theoretical reasons to be interested in borders, and how they affect international relations.

Clearly, a key dimension for many researchers is proximity (see for example, Gochman's 1992 discussion of borders as they relate to the overall COW project). The diffusion research of Most and Starr (e.g., 1980) moved to the study of borders after concluding that the diffusion of certain phenomena could only be studied by looking at units that were "relevant" to one another-- and that such relevance could be indicated by geographical proximity (see also the work of Lemke-- 1995, 1996). Proximity, in turn, could be operationalized through "borders." Borders were seen as important indicators of proximity because they had important relationships to both the opportunity and willingness of state actors as conceptualized by Starr and Most (1976). One key aspect of borders is that they affect the interaction opportunities of states, constraining or expanding the possibilities of interaction that are available to them. States that share borders will tend to have a greater ease of interaction with one another, and thus will tend to have greater numbers of interactions. This idea developed from multidisciplinary sources, such as economist Kenneth Boulding's (1962) concept of the loss-of-strength gradient; or geographer G.K. Zipf's (1949) "law of least effort." The important issue raised here is that borders create the opportunity for interaction (see Starr and Most 1976, Most and Starr 1980, and Siverson and Starr 1991 for a full discussion of geographic opportunity).

Such opportunity might be seen in terms of the number of other countries with which any single state has interaction opportunities. It might also be seen in the degree to which such opportunity exists between any particular pair of states. So, for example, Wesley (1962) argues that the length of a common border between two countries is a better measure of "geographic opportunity" than simply the number of borders. One of the authors has argued elsewhere that the opportunities for interaction view of borders gets at the important conceptual core of proximity in a way that other measures of "distance" do not.

Secondly, borders also have an impact on the willingness of decision makers to choose certain policy options, in that they act as indicators of areas of great importance or salience. Because other states are close, having greater ease of interaction and the ability to bring military capabilities to bear, they are also key areas of external cues (or diffusion). Accordingly, activities in these areas are particularly worrisome, can create uncertainty, and thus deserve attention. The notion that changes in bordering areas create uncertainty because of their proximity is based on arguments developed by Midlarsky (e.g., 1970, 1975), and applied in Most and Starr (1980). Starr and Most (1976, 10) are also particularly concerned with the "roles that different types of borders appear to play" in war involvement. Different types of borders might have differential impacts on both opportunity and willingness. Thus, borders are differentiated in terms of homeland borders and borders generated by colonial territories. This differentiation allows analysts to test whether all territory is seen as equally important, or whether homeland territory generates greater willingness than more distantly held colonial/imperial territories. Implicitly tested in such analyses is the notion that it is homeland territory per se, that is important: that the proximity of any homeland territory of one state to any homeland territory of another state is the important factor

Part of the considerable research devoted to borders and territory suggests that territorial contiguity is a major determinant of whether or not a state will go to war with another state. Indeed, as a significant piece of the war puzzle, Vasquez suggests that territorial contiguity is the “source of conflict most likely to result in war” (Vasquez 1993, 307). However, perhaps simple contiguity may not be the critical factor. Dropping one level of analysis lower, Vasquez (1993) also hypothesizes that the nature of the border between two states affects the probability that states will go to war. Specifically, he hypothesizes that borders that coincide with natural frontiers or that traverse uninhabited regions or are seen as having little value are much less likely to provoke wars than dissimilar borders and border areas (this is a theme picked up later by Lemke).

Nonetheless, arguments can be found in the literature to suggest that just the opposite is true. Highly permeable and salient borders may produce qualitatively distinct behavior. For example, the ease of interaction and salience of border areas in northwestern Europe has– based on Deutsch’s social communication model of integration– most likely contributed to the area moving from high levels of conflict to high levels of cooperation. Relations between states with highly permeable and salient borders have shown a tendency toward interdependence/integration, making military conflict less likely and agreement more likely. For Karl Deutsch, transaction flows were central to the process by which integration took place and security communities were formed. According to Deutsch, countries are “clusters of population, united by grids of communication flows and transport systems, and separated by thinly settled or nearly empty territories” (as cited in Dougherty and Pfaltzgraff 1990, 435). The Deutschian study of how countries become integrated focuses on these transaction grids. Continuous communication and transaction linkages are presented as one of nine conditions for the creation of security communities.

Also citing Deutsch, Cobb and Elder (1970, 8) go straight to the essential relationship: “The third basic notion from communications theory is the idea that ‘transactions flow... establish[es] mutual relevance of actors. An actor with whom you have very much to do is relevant to you...’ Given this assumption, the level of interaction, or transaction, between the members of two social units may be taken as a behavioral measure of their mutual relevance.” They further observe (Cobb and Elder 1970, 24): “Deutsch ... finds that all successful security communities have a multiplicity of transaction channels performing a variety of common functions and purposes. Indeed, a high rate of transactional exchange within an area may mean that the community achieves a degree of integration...” The results of Cobb and Elder’s empirical study link the exchange of transactions to mutual relevance and then mutual relevance to greater levels of interstate collaboration.

For Russett (e.g. 1963), the mutual relevance of integration leading to a security community is represented by “responsiveness”– or, “... the probability that requests emanating from one state to the other will be met favorably” (Russett 1974, 329). In looking at integration defined as either responsiveness or security communities, Russett (1974, 335) finds that transactions describe integration, predict integration, make integration possible, and even cause integration.

Given the role of transactions in Deutschian models of integration, and their potential as indicators of growing interdependence and/or integration, then greater ease of interaction along a border also generates opportunities for positive interaction as well as opportunities for conflict. It is the latter relationship that was central to the Most and Starr (1980) interaction opportunity model, measured simply by the presence or absence of a border.

Thus, two sets of specific testable hypotheses are extant in the literature regarding the impact of the “nature” of borders on conflict. These hypotheses can be phrased as

• the easier a border is to cross, the greater the likelihood that the border will be a dispute border–Vasquez;

• the more salient a border is, the greater the likelihood that the border will be a dispute border–Vasquez;

• the easier a border is to cross, the less likelihood that the border will be a dispute border–Deutsch;

• the more salient a border is, the less likelihood that the border will be a dispute border–Deutsch.

Both sets of hypotheses push scholars to move beyond the simple “on-off” indicator of contiguity. Nonetheless, both sets of hypotheses postulate mutually exclusive monotonic relationships.

Complexity has become a turn of the century by-word, and the dynamics conditioned by the nature of borders are likely anything but simple. Clearly, relevant dyads and relevant neighborhoods are important steps forward in testing many extant theories. Willingness is simply not enough; opportunity must also exist. Thus, Vasquez argues that natural frontiers and borders of regions seen as having little of importance are less likely to generate conflict–less opportunity and less willingness to fight. However based on Deutsch, ease of interaction may generate both opportunities for conflict but also integration and therefore less willingness to fight. We propose that both the Vasquez and Deutschian hypotheses are independently incomplete. However, the insights of the two can be combined in a potentially powerful explanatory model. Rather than the relationship between the “nature” of borders and conflict being monotonic increasing or decreasing, we propose that the relationship is concave: the lowest levels of opportunity and border region salience should correspond to proportionally low incidences of conflict as should the highest levels of opportunity and border region salience, while the middle range of opportunity and salience should have proportionally the highest incidences of conflict. Thus, the analysis which follows tests each of these three rival hypotheses.

This paper continues a project that has applied the use of geographical information systems (GIS) to the study of geopolitics (see, for example, Starr and Bain 1995, Starr 2000; Forthcoming). Using the opportunity and willingness framework and its ideas concerning interaction opportunities, this project has attempted to reconceptualize borders by creating new measures of ease of interaction (opportunity) and salience/importance (willingness).

The GIS project builds upon these two dimensions of borders as indicators of proximity, to revise and reconceptualize how borders may be seen and measured. Using GIS has permitted a much fuller and clearer specification of borders by allowing us to talk about the specific qualities of borders in terms of opportunity and willingness. The GIS methodology, however, must be driven by theoretical considerations. Out of the hundreds of variables found in the 16 data layers of the ARC/INFO GIS (based on the 1992 Digital Chart of the World), only a few have been selected for the creation of the two indexes of ease of interaction and salience. This selection has been made in terms of basic theoretical issues found in both the international relations and the geography literatures.

Regarding opportunity, the notion of ease of interaction derives from Boulding's (1962) concern with the "loss-of-strength gradient," and the ability to project conventional military power. Out of the welter of possible variables (and taking various technical/analytic constraints into account), three central factors for the movement of land-based military capability have been selected-- the existence of roads, railroads, and the steepness of terrain. Based on the work of Boulding, Bueno de Mesquita, and Lemke, an index created from these three factors both reflects ease of interaction, and is applicable (valid) across a large set of international dyadic boundaries. An index has been created which simply notes the presence or absence of roads and railroads, and represents the hypsography or slope of terrain.

This creates a simple combined 1 to 4 index, with 4 representing the greatest ease of interaction, and 1 the most difficult areas to move across; (see the Appendix). While the GIS is also used to generate maps, which are an important medium for the visual presentation of results, more importantly analysts now have a way to represent any border (or section of any border) by a value from 1 to 4: values that can be used in data analyses within the GIS, both with other GIS variables or any other data sets that are imported into the ARC/INFO GIS.

Both the maps and the dataset can be used to demonstrate that the ease of interaction can vary along any single border that a state might have with a contiguous neighbor. The opportunity for interaction variable can be used to indicate this variation along any single border (or "arc", for example Israel's border with Lebanon). This would capture the variation that might occur on a very long border-- any particular portion of a border can be thus be characterized as to its degree of permeability. Thus, we are now able to go beyond the simple "on-off" characterization of contiguity; go beyond the simple idea that contiguity provides the possibility for interaction. While some parts of some borders would make this highly likely or possible, other parts would make interaction much less likely. We can make such judgments regardless of the length of a border, or the number of different borders that a state might have.

Willingness is represented by the salience dimension of borders. Salience is concerned with the importance or value of territory along or behind a border. Again, the question is how importance/value is to be measured. Here we must be concerned with indicators which would discriminate the level of value or concern over territory (as Starr and Most [1976] did by differentiating between homeland territory and colonial possessions; and between contiguous land borders and across-water borders). Drawing once more on geographers, demographics are seen as important: the territory on which a state's population lives. This is operationalized by areas of population concentration. A capital city, the locus of governmental activity and the symbol of the state, should also be used to indicate the importance of territory. Note that in selecting areas of population concentration and the seats of government we have now captured all three of the central elements of the state found in the international relations literature: territory, population, and government. Other coverages provide the location of items that indicate the importance of an area. For instance, active civil and military airports are identified, as well as such items as: military camps, forts, oil wells and refineries, power plants of various kinds, water tanks, factories, industrial complexes, hospitals, telecommunications stations, etc. The wide variety of items taken from the GIS are used because the substantive importance of any single type of installation can vary considerably across states. By identifying the location of key aspects of a state's transportation, communication, energy production, industrial, agricultural, and security infrastructures, we have items that tap "importance" in a manner generally relevant to all states.

The salience or importance of a border area is determined by places of population concentration, state capitals, airfields, and selected cultural features located within a 50,000 meter buffer of the region's borders. Capital cities are automatically coded with the highest value found in any of the units of analysis. Each feature identified has been given a value based on the number of other features that fell within 4 kilometers of it. These can then be mapped based on the value, showing where clusters arose. The maps provide graphics which represent the numbers of points that overlap within four kilometer ranges. Again, any area in a buffer around a border can now be characterized by a value from 1 to 4, which can be utilized in data analyses. A four value scale has been created, again with 4 indicating areas of the greatest salience, 1 indicating those areas with the least. As with opportunity for interaction, this representation of the salience of borders permits us to differentiate whole borders, to differentiate portions of long borders, and to make sense as to why some borders might be seen as more important than others; why changes or events across some borders might generate more uncertainty than occurrences across other borders.

Having generated indexes for ease of interaction and for salience, these have been combined into an index that indicates the existence of what has been called a vital border. Recall that Most and Starr (1989) argue that opportunity and willingness are jointly necessary conditions for certain types of behavior, and that they are related to each other in complex ways. The core of the vital border concept is that an arc or a border segment may combine high or low values reflecting both opportunity and willingness. Again, scores of 4 indicate a high level of "vitalness" and with 1 indicating the lowest level for the combined indexes (see the Appendix).

For each of the 301 contiguous land borders between states, 17 variables have been developed, which can be transformed into a variety of nominal, ordinal, and interval measures. For any dyad border (see the example of Israel's borders used in Table 1) we can present the length of that border in kilometers, and the area under the buffers created from that border. From these two variables we can present the percentage of each border that falls into categories 4 through 1. This can be done for ease of interaction, saliency, or vitalness. Knowing the length of the arc, the area under the buffer along it, and the percentage of each category, permits the analyst to use interval data (as noted below) or broadly based categories such as high-salience or low-salience. Note also that Table 1 provides a weighted average for each border in terms of ease of interaction, salience, or vitalness, showing the average value across the whole border.

This global dataset derived from the GIS analyses includes 151 states with land borders, which generate 301 separate contiguous land borders between states. The states in this group thus average almost four borders each. Table 2 provides descriptive data on the total set of borders, using the weighted averages. For example, we see that the average salience is quite low, barely getting above 1.000 (with a maximum value of 1.369 on the 4.000 scale). This means that although we find many areas with a value of 4 along borders, they constitute only very small portions of the total border. The values for ease of interaction are much higher (thus, so are the values for vitalness). Interestingly, the border with the highest salience score exists between Moldova and the Ukraine. In many ways this should not be surprising since until less than a decade ago, this was only an internal border, or the equivalent of the border between Connecticut and Massachusetts. With a weighted average of 1.342, the German-Dutch border is the next highest. A cluster of relatively high salience borders are found among the original members of the EEC. And, because of a high density of road and rail facilities, they also have among the highest weighted averages in terms of ease of interaction.

That is-- the borders of the original core countries of the EU also have borders that look like the internal jurisdictional boundaries of states, in terms of both salience and ease of interaction.

Above we introduced two views of territorial proximity, contiguity, and interaction opportunity. The new dataset that has been generated from the ARC/INFO GIS– with new operationalizations of opportunity and willingness as ease of interaction and salience– now permits us to evaluate empirically the theoretical claims of the two seemingly distinct bodies of literature and hypotheses. Which finds the greatest support? Or, more interestingly can both be only partially true? In order to give both sets of hypotheses an equal opportunity and to allow for the possibility that both may be partially true, the border measures have been divided into three categories: borders falling in the lowest 20 percent of weighted measures for ease of interaction, salience, and vital; borders falling in the middle 60 percent of weighted measures for ease of interaction, salience, and vital; and borders falling in the highest 20 percent of weighted measures for ease of interaction, salience, and vital.

The expected outcomes based on each of the hypotheses are shown in Table 3. If the Vasquez hypotheses hold, then one would expect to see the lowest levels of conflict for the lowest 20 percent of cases (measured as ease of interaction, salience, and vital), and the highest levels of conflict for the highest 20 percent of cases. If the Deutschian integration/interdependence hypotheses hold, then one would expect to see the highest levels of conflict for the lowest 20 percent of cases, and the lowest levels of conflict for the highest 20 percent of cases. Finally, if both hypotheses sets have partial merit, as we suggest, then one would likely see low levels of conflict for both the upper and lower 20 percent but relatively high levels for the middle 60 percent.

One major assumption of this project is that the border data generated (from the 1992 Digital Chart of the World) can be usefully applied backward for 20 to 25 years and forward for at least a decade. In other words, we assume that the data retain validity as a rough surrogate for the ease of interaction and salience of areas for this time frame. Therefore, subsets of two conflict datasets have been selected for the analyses based on this time frame. Enduring rivalries found in Goertz and Diehl (1993; 1995) that fall into the broad temporal band covered by the GIS data as well as Militarized Interstate Disputes (MID) between 1981 and 1992 provide two different conflict data sets with which the hypotheses can be tested.

Use of the two different data sets allows one to more thoroughly probe the effects of borders on conflict. Although some overlap exists between the contiguous border conflict dyads identified by both data sets, on the whole, the two data sets are characterized by different types of behavior. The enduring rivalries found in the work of Goertz and Diehl (1993; 1995) represent stable patterns of international conflict involving frequent violent clashes between the protagonists. Alternatively, cases taken from the MID data set represent every MID that takes place across a contiguous land border and has a some form of militarized action.

Since the focus of the study is the conditioning effect of the nature of contiguous borders on conflict, even though multiple MIDs may exist between the same two countries, the border is simply coded as having been a MID border. This results in 91 different MID and 22 enduring rivalry contiguous land borders. The enduring rivalry dyads allow us to examine frequent escalations to violence between the same parties, while the MID dyads allow us to look at conflict escalation more broadly.

Each of the 301 contiguous land borders has been coded as either being an enduring rivalry border (Yes) or as not being an enduring rivalry border (No). If the borders do not condition enduring rivarly behavior, then the distribution of enduring rivalry borders should be proportional to the distribution of borders as a whole. Specifically, if enduring rivalry behavior is statistically independent of the “nature” of contiguous land borders, then between four and five of the 22 enduring rivalry borders should be in the lowest and highest 20 percent of “vital” borders. Similarly, between four and five of the 22 enduring rivalry borders should fall into the categories of the 20 percent representing the most difficult borders to cross and the 20 percent representing the easiest borders to cross. The distribution of enduring rivalry borders across the categories representing border salience will be the same if, indeed, enduring rivalry behavior is statistically independent of border salience. The Crosstab results for enduring rivalry borders and “vital”, ease of interaction, and salience are shown in Tables 4, 5, and 6 respectively.

Regarding Most and Starr’s (1989) assertion that opportunity and willingness are jointly necessary conditions for certain types of behavior, the presence or absence of enduring rivalry borders appears to be affected by how vital borders are, as shown in Table 4. Of the 60 least vital contiguous land borders in the world, only two are enduring rivalry borders. Proportionally, this is less than half of what one would expect. Similarly, only one of the 60 most vital contiguous land borders in the world is an enduring rivalry border. The probability of seeing this distribution by chance is approximately p=.031. Thus, we are indeed led to believe that the “vitalness” of a border affects the likelihood that the border will become an enduring rivalry border. However, neither the Vasquez nor Deutschian hypotheses completely hold. The relationship depicted in Table 4 is the inverted U-shaped relationship that we hypothesized: the combination of constrained opportunity through limited ease of interaction and low salience does reduce the probability of a border becoming an enduring rivalry border, yet so does the combination of easy interaction and high border salience. The highest probability of a border becoming an enduring rivalry border lies in the middle region.

Turning to the individual effects of ease of interaction and border salience on the probability of a contiguous land border being an enduring rivalry border, we see the same dynamics exhibited. One can see in Table 5 that enduring rivalries are less likely than expected to take place across borders with measures of ease of interaction in either the lowest or highest 20 percent. The probability of seeing this distribution of cases by chance if the occurrence of enduring rivalries is independent of the ease of interacting across a border is p=.049. Thus, the occurrence of enduring rivalry does appear related how easy a border is to cross, and the relationship depicted in Table 5 is again the hypothesized inverted U-shape. Although the relationship shown in Table 6 is slightly weaker–the probability of seeing this distribution of cases by chance if the variables are statistically independent is p=.085–the deviations from the expected values match those predicted by the inverted U-shape hypothesis.

Therefore, the occurrence of enduring rivalries between parties with contiguous land borders does appear to be directly related to the “nature” of the shared border. Enduring rivalries show a statistical dependence on all three weighted measures of the “nature” of borders developed in the GIS project. Furthermore, the relationship appears to be more complicated than previously hypothesized. Rather than finding a simple monotonic increasing or decreasing function in the data, we have found that the relationship is concave. The greatest likelihood of a border being an enduring rivalry border occurs in the middle ranges of “vitalness”, ease of interaction, and salience.

Although the occurrence of enduring rivalries between contiguous parties appears dependent upon the nature of their shared borders, the occurrence of other types of militarized interstate disputes between contiguous parties may still be independent of the “nature” of their shared borders. Consequently, this possibility is explored in Tables 7, 8, and 9. In all three Tables as with enduring rivalry borders, if a contiguous land border sharing dyad has had an MID, the border is coded as “Yes.” If not, then the border is coded as “No.” The categories for the lowest 20 percent, middle 60 percent, and highest 20 percent remain the same from the previous analyses.

For each of the three variables, the relationship between the nature of the border and militarized conflict behavior is even more pronounced than it was for enduring rivalries. However, unlike the results for enduring rivalries, the distribution of cases for the variable “vital” has the highest probability of occurring by chance, p=.023. Nonetheless, this probability remains sufficiently low that one can confidently say that militarized interstate dispute behavior is conditioned by the “nature” of shared land borders. The remaining probabilities are p=.006 for ease of interaction and p=.013 for salience.

Once again, none of the three Tables reveals dynamics predicted either by Vasquez or the Deutschian integration models. Rather, each of the three Tables show that MIDs exhibit behavior corresponding to the combination of the Vasquez hypotheses with the Deutschian integration hypotheses. All three Tables clearly reveal the hypothesized inverted U-shape relationship. For example, whereas the expected count of MID borders in the lowest 20 percent of “vital” borders is18.1, the actual count is 15. Similarly, this is the expected count of MID borders in the highest 20 percent of “vital” borders, while the actual count is only 11. The differences are more extreme for the remaining two variables.

Assuming the apparent relationships are not spurious, these results suggest a number of important points. First, governments appear less likely to act/react over low salience border areas. These include borders that exhibit relatively low population concentrations and, compared to the length of the border, a dearth of infrastructure. Strong arguments have been presented by Vasquez, Goertz and Diehl (1992), and Huth (1996), among others, that it is territory per se which generates conflict and war, both as the issue over which war breaks out, and as a factor which increases the stakes of a war. These arguments are based on the proposition that it is territory-- any territory-- which creates an opportunity for conflict, which serves as the issue for war, and which makes the stakes worth fighting over. These arguments are not supported by the inverted U-shaped findings presented here– especially by the level of conflict found for the lowest 20 percent in regard to salience.

Second, and quite interestingly, border length fails as a competing explanation for why governments fail to act/react over low salience border areas: of the thirteen MID borders in the lowest 20 percent of salient borders, seven have above average length, while six have below average length. Third, high border salience makes dispute escalation to military conflict unlikely. Governments rely on other means of resolving disputes with countries neighboring vital border areas. Both of these conditions dampen the probability for escalation to military conflict.

Fourth, Lemke’s (1995) concern for relevant neighborhoods finds moderate support in that governments are less likely to turn to military action in the face of physical constraints on mobility. Low ease of interaction reduces the probability of a border becoming a MID border. Fourth, the surprisingly low probability of a high ease of interaction becoming a MID border suggests that as cross-border interaction becomes easier, transaction flows are also likely to increase thereby contributing to the creation of a security community. Although other explanations may exist, states appear much less likely to escalate a dispute to military action with neighboring states sharing porous borders.

Given that both salience and ease of interaction condition dispute behavior in the same manner, the mirroring of these effects in the overall measure of border vitalness is not surprising–one should not expect that changing the logical “OR” to “AND” should also change the observed behavior. Governmental dispute behavior is affected by the degree of border “vitalness.” Neighboring countries sharing less vital border areas likely receive less governmental attention, fewer meaningful events are likely to occur along such borders. However, past a certain threshold of shared border “vitalness”, governments appear much less likely to escalate a dispute to military action.

Borders matter. Proximity remains an important conceptual variable in the study of major power general war, the diffusion of international conflict, and crisis behavior. Whether or not states share borders has been a principal means of operationalizing proximity. However, a shared contiguous land border may not adequately reflect the expected underlying dynamics. This study has examined the utility of moving beyond a simple “on-off” dichotomous view of contiguous land borders to examine the terrain and human activity along shared border areas.

For each of the 301 contiguous land borders between states in the international system, measures of ease of interaction, salience, and overall border vitalness have been developed using GIS. Each border segment has been categorized along these dimensions with measures ranging from 1 to 4, with 1 being the least vital, least salient, least easy to cross and 4 being the most vital, most salient, most easy to cross. Based on the lengths of the border segments falling into each category weighted average measures of vitalness, salience, and ease of interaction have been created for the 301 borders. These weighted measures provide an exciting opportunity to move beyond the “on-off” characterization of contiguous land borders.

Two major lines of thought are extant in international relations literature regarding the expected effect of the “nature” of borders on interstate behavior. Work by Vasquez (1993) and Lemke (1995) suggests that conflict is more likely across easier to cross borders than difficult to cross borders. Similarly, high importance borders areas are expected to generate greater conflict than low importance areas. Thus, one should find increasing monotonic relationships between ease of interaction and the likelihood of conflict and border salience and the likelihood of conflict. However, another body of literature suggests just the opposite: based on Deutsch’s ideas of transaction linkages and security communities, higher ease of interaction and border salience should reduce the likelihood of conflict (Russett 1974). We propose that both approaches are partially correct and that the highest levels of conflict are found in the middle ranges of ease of interaction, salience, and vitalness.

In order to test the three rival hypotheses, subsets of Goertz and Diehl’s (1993;1995) enduring rivalry data and the MID data were selected to match the broad temporal band covered by the GIS border data set. These two data sets cross the spectrum of militarized dispute action. The MID cases represent behaviors from threats to use force to war, while the enduring rivalry data reflects repeated escalation to violent conflict. On the basis of our analyses of these two sets of cases in conjunction with the weighted average measures of ease of interaction, salience, and vitalness, we conclude not only that the “nature” of contiguous borders matter but also that the combined hypotheses receive the greatest support from the data.

Such results, therefore, provide evidence that scholars should be moving beyond the simple dichotomous “on-off” view of contiguous land borders to look at the nature of shared land borders. Failure to look beyond the presence/absence of shared borders will lead to model misspecification and an overall loss of model power. A border is not a border is not a border. Territory, per se, does not automatically becomes a reason for conflict (a la Vasquez) nor does it automatically create greater opportunity for conflict (a la Most and Starr 1980). Some types of borders are dramatically less likely to lead to military conflict than others, and scholars need to account for these differences.

The dataset used in this research was created from the ARC/INFO GIS housed in the Collegeof Liberal Arts Computing Lab at the University of South Carolina. Data for this project is from the Digital Chart of the World (DCW), produced by ESRI for the Defense Mapping Agency in 1992. The data contained in the DCW was derived primarily from maps in the Defense Mapping Agency Operational Navigation Chart series that were used to generate a 1:1,000,000-scale vector database covering the entire surface of the earth. Because of the enormous spatial areas and quantities of data associated with the DCW, data is organized and stored in 2,094 five degree (latitude-longitude) square tiles. All data, at the 1:1,000,000 scale, for a given area of the world is stored in its corresponding data tile.

The Opportunity for Interaction/Ease of Interaction index was developed as follows:

The first variable looked for the presence or absence of roads within the locations being studied. Roads included multi-lane divided roads, as well as primary and secondary roads (Layer 4, Road Layer, RDLINE). The second variable was the presence or absence of railroads (Layer 3, Railroad Layer, RRLINE). The third variable involved the slope of an area, which was based on the elevation values of contour lines (in mean feet above sea level; Layer 8, Hypsography Layer, HYNET), and was derived from a digital terrain model by converting the hypsography into a triangulated irregular network. Each of these values was investigated for a buffer area of 50,000 meters on each side of all international borders.

Areas of urban concentration including urbanized areas and capital cities were extracted from the Populated Place Layer, Layer 2 (PPPOLY and PPPOINT). Other coverages provided the location of items that would indicate the importance of an area. For instance, from Layer 13, the Aeronautical Layer, active civil and military airports were identified (AEPOINT). The Cultural Landmark Layer (Layer 14) provides a catalogue of such items as noted in the text.

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TABLE 3: Hypotheses on the Probability of Conflict Based on the Nature of Borders^*

	Border Ease of Interaction, Salience, and “Vitalness”
	Low	Medium	High
Vasquez	CONFLICT	CONFLICT	CONFLICT
Deutsch	CONFLICT	CONFLICT	CONFLICT
Starr and Thomas	CONFLICT	CONFLICT	CONFLICT
^*The increased likelihood of conflict is visually depicted by an increased font size

			Goertz and Diehl Enduring Rivalry Border		Total
			No	Yes
“Vital” Borders in Three Categories	lowest 20%	Count	58	2	60
		Expected Count	55.6	4.4
		% of Total	19.3%	.7%	19.9%
	middle 60%	Count	162	19	181
		Expected Count	167.8	13.2
		% of Total	53.8%	6.3%	60.1%
	highest 20%	Count	59	1	60
		Expected Count	55.6	4.4
		% of Total	19.6%	.3%	19.9%
Total Number of Borders		Count	279	22	301
		% of Total	92.7%	7.3%	100.0%
χ²=6.935, p=.031

TABLE 5: Enduring Rivalries and Ease of Interaction Across Contiguous Land Borders

			Goertz and Diehl Enduring Rivalry Border		Total
			No	Yes
Ease of Interaction in Three Categories	lowest 20%	Count	58	2	60
		Expected Count	55.6	4.4
		% of Total	19.3%	.7%	19.9%
	middle 60%	Count	168	19	187
		Expected Count	173.3	13.7
		% of Total	55.8%	6.3%	62.1%
	highest 20%	Count	53	1	54
		Expected Count	50.1	3.9