World War I plays a central role in many of the theoretical debates among scholars of international politics. Taking advantage of recent advances in game theory and the latest historiography, Frank C. Zagare offers a new and provocative interpretation of the events that led to the outbreak of a world war in August 1914. He analyzes key events from Bismarck's surprising decision in 1879 to enter into a strategic alliance with Austria-Hungary; to the British attempt to ensure peace; to the German invasion of Belgium and France; and finally, to the escalation that culminated in a full-scale global war. Zagare concludes that, while the war was most certainly unintended, it was in no sense accidental. Along the way, key decision makers in all the pertinent capitals made calculated choices that may have been wrongheaded but that were also rational. Yet, until the very end, the war was not inevitable. There were alternative rational courses that did not necessarily imply conflict. With different leaders or with different policies, the war could have been averted. The Games of July serves not only as an analytical narrative but also as a work of theoretical assessment. Standard realist and liberal explanations of the Great War are evaluated along with a collection of game-theoretic models known as Perfect Deterrence Theory.