I'm not an expert on the topic but I'll share my two cents... WWII really pushed America completely out of the Great Depression. During that time, the US manufactured a ridiculous amount of weapons, airplanes, etc. for herself and her Allies. The US was making so much that it outproduced all of the other players combined. Even Hitler thought that the Americans saying how they were going to produce over 180,000 airplanes was just propaganda. By the end of the war, America had produced around 300,000 airplanes; an amazing feat. All of this meant more jobs, and a booming economy when the other countries had to pay the US back for their products.

Besides, the other main powers of the world, such as the UK, Japan and Russia, were all war-torn. They had a ton of rebuilding to do after all the bombings and ravaging of war, which cost a lot of money. America didn't really have to invest in building or infrastructure, because the war didn't take place on American soil.

The British Empire, which was arguably the main power before that point, started to dissolve. During the war, the Empire was stretched very thin, and it couldn't protect every single border like it wanted to. After the war, the Empire was out of money, and really needed to rebuild its home, forcing the decolonization and dissolution of the British Empire.

So basically, America was a powerhouse when it came to manufacturing, and it didn't have to do very much rebuilding after the War. A lot of these other countries had to pay the US back, and rebuild after bombings, and the consequences of war on infrastructure.