What events that shifted American involvement in World War 2?

Several key events shifted American involvement in World War II, most notably the attack on Pearl Harbor on December 7, 1941, which prompted the U.S. to declare war on Japan the following day. This attack galvanized public opinion in favor of entering the war, leading to a formal alliance with the Allies. Additionally, the growing threat from Axis powers in Europe and the Lend-Lease Act, which allowed the U.S. to supply military aid to Allied nations, further solidified America's commitment to the war effort.