Why did the united states stay out of world war 2 at first

That is because there were no compelling reason for them to be in it in the first place.

The majority of Americans felt that the United States should stay out of World War I because it was not a signatory to any of the agreements that had lured the European powers into conflict across the continent, so President Woodrow Wilson declared a neutrality policy, attempting instead to broker a peace agreement. Even when a German sub sank the British ocean liner Lusitania in 1915, with 128 Americans on board, the United States demanded a stop to the destruction of passenger ships, and Germany agreed, leading to continued American neutrality.