1. what factors contributed to the united states becoming a world leader?

I'd say our economy is the biggest factor, as because it has allowed our GDP to increase, and from all that money, the U.S was able to increase military power and research. I'd also guess it's because we're a democracy.

It's also because of the several wars the U.S has been in and won, including WWII.
Our allies have also helped us, and now we have big alliances with other countries