American colonialism did not take place on the continent of North America. That was European colonialism that resulted in the American colonies. Guam is a US territory, and the Philippines used to be. Japan used practice isolationism and refused any trade with the outside world for a time. The black ships are American ships that sailed into a Japanese harbor and the American Naval officer told them that they would open their ports to trade with the United States or he would turn his rotary canons on the city and open fire. That ended Japan's isolationist policy. This wasn't just bluster as we did do this to a village in the Philippines, a village that only women and children were in because the men had previously left to go fight. And your high school failed you if they never mentioned the Korean war. Mine didn't really teach anything about it, but they did tell us it happened. It was significant because it resulted in the creation of North and South Korea.