UC San Diego

Since World War II, less than a third of all interstate wars have ended in peace treaties. Instead of countries making formal concessions, fighting often ends with cease-fires that leave forces in place without belligerents resolving their underlying conflict. Before World War II, however, fighting was usually quickly followed by a peace accord, in which defeated countries formally renounced political claims--usually regarding sovereignty over territory. So why do adversaries no longer end hostilities with peace accords, opting instead for long-term cease-fire agreements?

I contend that as the territorial integrity norm became increasingly robust, it weakened the victor's outside option and strengthening the bargaining position of the defeated by making unilateral annexation of conquered territory far more costly. At the same time, the norm made formal concessions far more permanent, as the defeated could no longer renege and re-conquer lost territory without incurring substantial costs for violating that same norm. Thus, the territorial integrity norm, precisely by making peace deal agreements more credible, made them harder to reach.

After exploring the historical development of the territorial integrity norm, I conduct quantitative tests of my theory using an original dataset I constructed for all interstate wars fought from 1816-2007. I find that neighboring states with settled boundaries before hostilities began are far more likely to sign peace agreements--and do so more quickly--than states with ex ante contested borders. Prior to the advent of this norm (i.e. before 1919), however, the opposite was true: having settled boundaries actually reduced the likelihood of signing a peace accord. I also find that the territorial integrity norm altered the terms of peace. Historically, peace accords granted winners new territory; but under the territorial integrity norm, peace accords now generally return belligerents to international (or antebellum) borders, or alternatively refer the dispute to third party arbitration.

If the territorial integrity norm matters, then strategically-minded states should anticipate no longer being able to invade their neighbors in order to conquer their territory. Testing this proposition for all neighboring countries from 1816-2001, I find as the norm became more robust, neighboring states with settled borders have become far less likely to go to war than similar neighbors with contested borders.