Alliance Norms and War: A New Piece in an Old Puzzle

The relationship between alliance aggregation and war is one of the most perplexing research questions within the field of international relations. We propose that by measuring the degree to which international norms support binding treaty obligations, a macroindicator of alliance commitment can be devised that is grounded in the cultural attributes of the international system, and that can be used in conjunction with indicators based on structural attributes to account for the onset of war. Based on the results from tests conducted on the European great power system of 1820–1914 and the central power system of 1820–1939, we conclude that peace is best preserved when there is a moderate amount of flexibility in the structure of alliances, and when alliance commitments are considered binding by prevailing international norms.