What event finally prevented americans from maintaining military isolationism in the period between 1914–1941?

America’s policy of military isolationism officially ended in 1941 after the attack of Pearl Harbor. This attack on a US military base in Hawaii was done by the Japanese military. This happened on December 7th 1941. A day after the attack, President Franklin D Roosevelt gave a speech to Congress asking them to declare war on Japan. Congress by an almost unanimous vote, declared war on Japan. This declaration of war is when the US started their involvement in World War II.

He droped it over the bridge into the river