What a perfect way to describe the situation. As they say in france, you have come up with le mot just.
There is a pervasive theme that runs throughout all imperialist cultures, from Rome to the Ottomans to Britain, and of course, to the U.S. The theme has many variations, but mongol hordes about to sweep across the boundaries is as good as any. You also have the image of the lonely fort out in the wilderness beset on all sides by barbarians about to rush in.
Imperialist mythology is budened with the need to reverse the roles that exist in reality. So, while Rome was out conquering the world, they had tons of myths about how Rome was beset on all sides by the mongol hordes about to rush in and destroy them, how Rome was just fighting for a breathing space in a world of enemies bent on their destruction. While Britain was out conquering the world, they had tons of tales in about the lonely fort out in the wilderness defending itslef against faceless hordes of brown people who for some reason want to kill them. And so on.
In general, the mythology reverses the roles. It wasn’t Rome that was being beset upon, it was Rome who was conquering the world. It wasn’t Britian that was being attacked by Africans, but vice versa. Likewise, it wasn’t the American Indians who were kicking white people off their land, but vice versa. Yet, it was the Indians who were called savages.
In recent history this type of mythology has been taken to new heights. It permeates corporate culture, typified in the Rambo movies, or Out of Africa, etc. You had all these myths about American MIAs in Vietnam, etc., propagated by the corporate culture. In the Rambo movies, you had the Vietnamese dropping napalm on the Americans, and not vice versa. These, and countless other examples, show how the actual roles are reversed in the mythology.
So, while in reality it has been the U.S. that has been the expansionist, in the mythology it is reversed. You have tons of movies, books, etc. about the USSR invading the U.S. In reality, the U.S. has never been invaded by the USSR, but the U.S. has in fact invaded the USSR. And so on.
In this particular situation, again, the roles are reversed. While it is North Korea that lives on constant fear of being invaded by the U.S. and its proxies, in the mythology it is the U.S.'s allies that have to be worried about being invaded by the oh-so-apt “mongol hordes.”