The main event that led the United State to take a more active role in the world affairs was World War II, since the US emerged from this war an economic superpower. It was also clear that some nation needed to "fill the void" left by the relative fall of the British Empire.
I'm pretty sure that they opened the first Silk Road
They did not get along that we'll so they had half of the land they wanted
The two types of sources are maps and artifacts
