What geographical circumstances make it easier for the United States to remain a dominant world power?

Answer 1

To the west we have the Pacific Ocean and to the east we have the Atlantic Ocean. Those are two nice boundaries that we don't have to patrol. We have friendly neighbors to the North and the South. We have a bread basket in the midwest that allows us to grow enough food to feed the entire world. We are very blessed.

Answer 2

Located on a continent away from the old world, the United States has not had to fight as many wars as its European counterparts. Being bordered by only two countries, Canada and Mexico, makes for a much easier and safer existence than being in the vicinity of tens of countries, and before them, communities, where proximity between different groups led to wars. Besides 9/11 (which was not a conventional attack), and Pearl Harbor (which was), the US mainland has remained fairly safe for a large part because there are no enemies geographically close by.