Alliances were an important feature of the international system on the eve of World War I. The formation of rival blocs of Great Powers has previously considered a major cause of the outbreak of war in 1914, but this assessment misses the point. Instead of increased rigidity, it was, rather, the uncertainty of the alliances’ cohesion in the face of a casus foederis that fostered a preference for high-risk crisis management among decision-makers.
