re ninety nine years had passed since the end of the last general European war the Napoleonic War in 1815. Ideological hatreds among nations were weak; the Imperial Germany of Kaiser Wilhelm II was rather militaristic and rather authoritarian, but not remotely to be compared with Nazi Germany a generation later, while the most authoritarian (even despotic) of the Great Powers, Czarist Russia, went to war on the same side as democratic Britain and France.
In short, by later twentieth century standards, the European Powers had no strong reason to go to war with one another in the fall of 1914. Yet they did, ending one age, and beginning another. Only in 1990, with the crumbling of Soviet Communism and the winding down of the Cold War itself ultimately derived from World War I, via World War II did the violent age that began in August, 1914, seem to be coming to an end.
Broadly speaking, two sets of explanations have been advanced as underlying explanations for World War I. They are independent, and not necessarily contradictory; admitting the truth of one does not invalidate the other. The first can roughly be called war by accident. According to this theory, none of the Great Powers really wanted war, but when a crisis became unmanageable, they did not know how to avoid it and did not realize how terrible it would be when it came. A classic exposition of this theory is contained in Barbara Tuchman's August, 1914. The other theory holds that World War I erupted because the European diplomatic system had failed to adjust to the changing balance of power among the major European (and by 1914, non European) nations. Fading powers clung to a status they could no longer uphold, while rising powers demanded their "place in the sun." When diplomacy failed to resolve the pecking order of the powers, the dissatisfied resorted to war. A major recent exponent of this theory was Paul Kennedy, in his Rise ...