Hallo, Jon15!
Well, the United States got involved in WWII because of many reasons. Mainly:
-The Japanese Navy attacked the US naval and air bases at Pearl Harbour at Oahu Island, Hawaii on December 7th 1941 an hour earlier than the Japanese declared war on USA. More than 3.000 Americans were killed and the Pacific Fleet of the USA was destroyed or damaged that day.
-On December 11th 1941, Italy and Germany, Japan's allies declared war on USA.
But if we add that the USA didn't want Germany ruling the whole European continent and the Japanese ruling the whole Pacific, then we can asure that the USA would have been involved in the war sooner or later, even if not attacked.
Hope this helps. If not. Ask more specific questions and I'll gladly respond them.
