What was the cause of US involvement in world war 2?

Answer 1

The United States became involved in World War II due to the attack on Pearl Harbor by the Japanesse. The United States had to act after the unprovoked and unwarned attack on one of its Military bases.

Answer 2

The USA joined the war when Japan attacked Pearl harbour December 7,1941

Answer 3

The Japanese attacked Pearl Harbor, Hawaii, prompting the Americans to declare war on them. The Germans, being Japan's allies, then declared war on the USA.

Answer 4

Basically it was the Japanese attack on the US Pacific Fleet at Pearl Harbor, Hawaii which brought it into WW2.