World War I: Nationalistic Bosnian assassians, supplied by the Serbian terrorist orginization Black Hand tried to kill Austrian Archeduke Frand Ferdinand, a few countries started arguing... and eventually it was everyone pointing fingers and saying "i'm gonna fight you because you fought my friend".
World War II: Germany was blamed for WWI, and world leaders came together to decide what to do, and decided to severly punish Germany. Once Germany learned of it's punishments and how it affected the country Germans/Germany became furious. One artist, who we know as Adolf Hitler, came up and said he could easily change the problems facing the Weimer Republic (Germany of the time). During this time, radicals could easily gain support because of how much people wanted change, and one such party that was active in this time was the Nazi Party. Hitler worked his way to become leader of the Nazi Party, and after tried to turn his reign into a dictatorship. He failed a coup and the successfully got to the top (meaning he could do what he likes) through legit means. After Hitler became a big fascist leader, he linked up with other fascists and everyone was basically waiting for Germany to make a move because world tension was super high.
<span>To expand the power of state governments</span>
WWII changed the US identity greatly. For one, it showed the rest of the world that they are a dominant force to be reckoned with. For another, it also showed that they would do what needed to be done to win battles, and more importantly, wars. It also disproved the thought that they were not a unified nation, and that they could work cohesively toward the same goal <span />
