I cynically think that neither China or South Korea want to deprogram 30 million brainwashed people, or absorb the land area that has (likely) barely functional infrastructure and no resources to exploit that would cover the costs of integrating the worlds largest cult into your nation and upgrading the infrastructure alongside it. I think each side is hoping the other one has to deal with it.

I doubt either of them have the capability to do it in the first place! Invading an industrialised, heavily armed country of 30 million people which has been planning for that to happen for decades is an extremely big deal. Note that it didn't go well in the Korean War, and North Korea is much more prepared for it now than then.

Are you saying that the Korean war started when North Korea was invaded? I was not under the impression that was the historical consensus.

No, definitely not. However, during the Korean War, UN/SK forces did invade North Korea.

That seems like an odd use of the word "invade". I mean, your definition is implicit, but I'm not sure it's quite standard.

If I search the internet for, say, "soviet invasion of germany" I get almost entirely hits such as plans for invading West Germany for WWIII, or alternate histories where the Soviets invaded Germany at the beginning of WWII instead of signing a pact. Also the German invasion of the Soviet Union.

It's not entirely unheard of to refer to Soviet offensive into Germany at the end of WWII as the "invasion of Germany", but it seems to be somewhat rare and unusual. And with Bing, unlike Google, I didn't find that usage at all.

I wonder if people rarely use the phrase because it seems vaguely to imply sympathy with the Nazis.