Final answer:
The US isolationism policy did not lead to the outbreak of World War II in Europe; it was factors like Hitler's expansionist policies and the failure of diplomacy that precipitated the war.
Step-by-step explanation:
What did not lead to the outbreak of World War II in Europe was the policy of isolationism adopted by the United States. While the rise of fascism in Germany and Italy, the annexation of Austria and the Sudetenland, and the signing of non-aggression pacts all accelerated Europe towards war, the U.S. tendency towards isolationism prior to the attack on Pearl Harbor did not directly provoke conflict in Europe. It was only after Japan's attack on December 7, 1941, that the United States was pulled from its isolationist stance into full participation in the war. Many factors, including Hitler's aggressive expansion and the failure of diplomacy, contributed to the start of the war, but America's pre-war isolation was more a factor in its delayed entry than in the initiation of war in Europe.