Why was us againts Germany in World War 2?

Answer 1

The simple answer is that Germany declared war on the US on December 11, 1941, four days after their Japanese allies had attacked the US.

In less than nine years since Hitler came to power the world had witnessed Hitler's actions, beginning with violating the Versailles Treaty, by rearming Germany, restarting a German Air Force (forbidden by the Treaty), and re-militarizing the Rhineland. Hitler had forced Austria to give up its independence and become a province of Germany. He then did the same to Czechoslovakia. He entered into a partnership with Stalin, and then invaded Poland. This last move caused Great Britain and France to go to war with Germany. Germany continued its conquests, invading Noway, Denmark, the Netherlands, Belgium, France and Yugoslavia before turning on the Russians and invading the Soviet Union, all before declaring war on the US.