When did US use the policy isolationism?

In the World War II era, the U.S. policy of "isolationism" ended quite abruptly. While President Roosevelt had lent aid to Great Britain in mild forms in 1940 and 1941, on December 7th of 1941, with the Japanese surprise attack on Pearl Harbor, the American people and leaders rose up vigorously to clamor for revenge, and thus American isolationism became a thing of the past.