The US changed its policies from an isolationist to interventionist. It supplied arms to the allied forces and emerged as a superpower by the end of WWII.
How US contributed in WWII?
The state has became an interventionist, it opened its economy and eliminated isolation. It provided arm support to the allied forces. By the time when other nations were rebuilding their infrastructures, US emerged as an industrial leader.
It emerged as a superpower by the way of technological and military advancements.
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