WW I began some thirty years prior with the political wranglings of Otto von Bismarck -- lots of "I'll cover your backside if you'll cover mine." The catalyst was the assassination of Archduke Ferdinand and his wife Sophie but the muslim Serb terrorist organization the Black Hand.
The foundation for WW II was layed with the Versaille Treaty ending WW I. It set in motion a whole slew of events that ultimately lead to Adolf Hitler's coming to power in Germany. Coupled with the expansion of Japan fueled by the Shinto religious belief that they were superior to everyone else and suddenly, you have the makings for a world war.
