Bringing the Thunder
North Korea has a very large standing army so I wouldn't totally disregard them. That being said, it's questionable how well-equipped that army is, as well as how many people would just desert it the second they step onto foreign soil due to the atrocious conditions in North Korea. I genuinely have no idea how indoctrinated/brainwashed the average North Korean soldier is, but the fact that many of them chose to brave a literal minefield patrolled by death squads to defect to South Korea tells me that they're probably not all that loyal to their crazy dictator.
Oh no, I'm not saying North Korea isn't a threat, just that the other three dwarfs its threat. NK has some weapons, but it doesn't have a superpower level military or economy to the point where it would stand a large chance of conquering nearby countries (of course their only mainland neighbors are South Korea and China which limits their path to expansion, but even then I don't think they're quite equipped to invade other countries in the same way as Germany or Russia was). North Korea is far less likely to win an "us vs. the world" sort of world war than the other 3.
I don't think a three-way alliance between the U.S., Russia, and China is all that likely in the near future, even under a Republican regime. Republicans universally despise anything they think even remotely resembles communism (and a whole bunch of stuff that has literally nothing to do with communism but Tucker Carlson said it does so it's bad), so major Republican support for Russia and China is unlikely on that basis alone.
Some Republicans have disturbingly been coming out in support of Putin and Russia, more than just Trump, I don't put anything past them as the only thing they truly seem to care about is money and power. They opposed communism in the Cold War because they didn't want Marxist philosophy putting ideas of fairer compensation and worker power in people's heads, but times have changed. Russia is no longer communist (and really the countries we identify as "communist" in the present day have more in common with Hitler than Marx), and Republican policy isn't really resonating with U.S. citizens so they're turning to fascism to retain control. Russia, China, and NK are closer to what the Republicans aspire to be, so I can easily see them siding with that faction should they gain power.