the policy of what kept the united states out of the fighting during the first few years of world war two

The correct answer is isolationism.

Isolationism was the policy wherein the United States would be generally disentangled from the world's affairs, but would especially be disentangled from the emerging wars in Europe and Asia during the 1930s.

The thinking was that America was still recovering from the Great Depression and had no business fighting for the interests of other nations abroad.