what event(s) helped lead the USA to the joining World War two ?

Answer 1

The aggression of Germany in Europe and Japan in the Pacific were viewed as threats to the U.S. Not only were some of our territories threatened, but our allies were being defeated. Of course when Japan bombed our naval base at Pearl Harbor in Hawaii, we immediately declared war on both Germany and Japan.

Check these sites for more information.

http://www.worldwariihistory.info/WWII/war.html

http://www.worldwariihistory.info/WWII/United-States.html

Answer 2

the japanese bombing pearl harbor is the answer