Why did the us become involed in world war 1?

The assassination of Arch Duke Franz Ferdinand in Sarajevo in 1914 was the catalist that started WW1. In 1917 u-boats sank the RMS Lusitania off Ireland with the loss of many American lives, propelling the US into the war against Germany. The british blockade of Germany in 1918 and the subsequent revolt by the German people, caused the navy to mutiny and the government to fall; ending the war.