The US committed most of her resources to the European Front, because the US followed the "Europe First!" Strategy, in which they defeated the stronger nation Germany and it's European Allies, before focusing on the Pacific Front. This is because many of America's allies generally were on the European side, and Germany had a better economy, army, generals, and technology, compared to Japan, making it so that a greater percentage of resources are needed to defeat Germany. Japan, on the other hand, did not build up much except for the navy, and so the Allies were able to fight a defensive war until Germany was defeated, before using the rest of their resources to defeat Japan.
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