What two wars have resulted from the multiple nationalities in Western Europe?

World War I; World War II. These two wars resulted from the clashing of multiple nationalities and multiple ideologies in Europe. World War I began when the Austrian archduke Franz Ferdinand was assassinated. There was belief that the Serbians had killed him, so Austria declared war. One thing led to another, and soon allies of both countries had been pulled into the war. That’s how World War I started.

World War II started slowly. It wasn’t a real powder keg, like World War I. Hitler had slowly been amassing land, annexing here and there. The rest of the world was taking a hands-off approach, telling him to stop but allowing him to take whatever it was that was causing a problem. That ended in 1939, when Hitler invaded Poland. The same powderkeg of allies got pulled in, and World War II began.