In 1648, the Peace of Westphalia replaced a system of overlapping authority with a system of clearly demarcated state borders. Two hundred years later and prompted by the French Revolution of 1789, Europe's popular revolutions transformed the state into the nation-state. This added a critical dimension to European affairs. With boundaries between nations having become as significant as borders between states, nations began to strive for the congruence of state and nation boundaries.

The nation-state doctrine gave rise to a new and often deadly kind of international conflict: irredentism. Seeking to reach congruence between the borders of the state and the boundaries of the nation, an unprecedented number of states started to claim territory from other states. Irredentist disputes frequently resulted in full-scale war. When former colonies were finally granted independence, the problem of irredentism started to surface outside Europe as well. The disputes between Pakistan and India over Jammu and Kashmir, Somalia and Ethiopia over the Ogaden, Israel and Syria over the Golan Heights, Argentina and the United Kingdom over the Islas Malvinas (Falkland Islands) are perhaps the best known among a very considerable number of cases.

Since the end of the Second World War, however, and in sharp contrast to Europe's past and other world regions, European states have shown a strong tendency to settle their irredentist disputes peacefully. There is even a consistent pattern of how they are settled peacefully.