What did Germany do that made the us join World War 2?

Answer 1

Germany didn't do anything to directly bring the US into the war. The US joined World War II because Japan attacked the American naval base at Pearl Harbor, Hawaii on December 7, 1941.

However, Germany and the US were not friends at the time- Germany was very belligerent and had been conquering other countries, which the US opposed. World War II started in September 1939, and the US was quietly supplying Germany's foes (mainly the United Kingdom) with weapons during the period between 1939 and the Pearl Harbor attack. Germany was allied with Japan since 1940, so when the US was attacked and declared war on Japan, Germany immediately declared war on the US.