It's not that simple. American presence on the Korean peninsula makes reunification efforts overly complicated. By some estimates, reunification would grow the Korean economy to be the third largest in the world. It would also give Koreans access to Russian pipelines and a large border with China. When climate change opens up arctic trade routes and frozen arctic resources, Russia will be in the position to benefit the most (although Putin relies too heavily on his tsarist-Stalinist strain of conservatism to be able to exploit the economy as efficiently as liberals or perhaps Chinese communists might). As convenient as it is to have a powerful ally in the U.S., the U.S. is no longer in a position where it can dictate the behaviors of foreign nations as it once used to, especially regarding China. That's simply a reality that Koreans have had to come to terms with, despite Americans seeming to believe that things can just return to how they used to be half a century ago.

Europe would do much better by defending itself on its own terms rather than perpetually hiding behind the Stars and Stripes. Hopefully Trump made it clear how dangerous that is.