In basic geometry, we learn that the perimeter is the sum of the length of the sides enclosing a geometric space. It is about as linear a concept as one could imagine, a mere matter of locating a space, measuring the length of the straight lines that define its outline, and adding it all up. In the natural world things get a bit more complex, with land masses segmented and defined by rivers and mountain ranges that do not lend themselves to the linear calculus of geometry. Still more complex, of course, are political boundaries, which are the legally and militarily enforced lines in the sand that set off a centrally-governed, territorially-contiguous political community (what we political scientists call a 'state') from its neighbors.
Once we recognize the invented nature of these political boundaries, even in those states which claim transcendent historical attachment between people and territory, we see that the perimeters, or the borders, of the state are designed not only to keep external enemies out, but to define who and what is worth defending within those barriers, and why that particular state has the legitimate right to do so. Rather than adding up the length of the sides of a geometric space to determine its value, the border-as-perimeter of a state is measured in less concrete terms that add up to state legitimation, such as sovereignty (autonomy from outside meddlers), security (from invasion) and identity (within the community and in contrast with outsiders). To paraphrase R.B.J. Walker's seminal work in this area, the state justifies its primary role in the international system and its monopoly over the use of force at home by mediating between the 'inside' and the 'outside' (2), and that mediation occurs -- literally and s ymbolically -- at the border.
This view of the international system of states as one of fortified units geared both internationally and domestically for continuous defense -- individually and in strategic alliances -- has been challenged in the immediate post-Cold War years by those proclaiming the rise of a community of 'liberal democratic states' that were no longer arming against one another, but rather opening their borders for economic (and, in the case of Europe, political) integration, often in regionally-defined spaces. In the vernacular of the constructivist literature with International Relations, which advocates for such a 'constructed' view of politics based upon the social transformation of identities, this is an expansion of the 'we,' a redefinition of the 'ingroup' to, if not fully include, then to no longer absolutely exclude those who are beyond a nation's strict political perimeter. (3)
There are three main hypotheses advanced to explain this cooperative turn in international relations, two of which stress the consolidation of a shared sense of identity across national boundaries. The neoliberal-institutionalist model posits that intensifying economic interdependence provides an incentive structure that makes cooperation a positive-sum outcome for competitive states; in other words, the classical liberal idea of 'peace through trade' is consistent with, and is advanced by, the rational calculations of power-maximizing units. (4) The second hypothesis is equally inspired by classical liberalism and by Immanuel Kant, but instead advances what has been called the 'democratic peace thesis.' (5) This is the notion that states with liberal democratic regimes are less likely to go to war against one another because their institutions are transparent (and thus avoid problems of mutual misperception), their armies are drawn from and funded by the population (the latter through taxes with the purse-s trings controlled by elected representatives in the legislature), and their leaders need popular support when they face re-election. Though not explicitly constructivist, the democratic peace thesis rests firmly on the assumption that democracies identify internationally with one another in a way that makes mutual interpretation of their foreign policy actions more likely to be sympathetic. …