I love the idea of Russia not annexing Outer Manchuria, and Manchuria becoming independent under the Qing dynasty in 1911 as a result. Definitely thinking on what I can contribute to this scenario.
However... why exactly are we talking about a modernized Korea that colonizes Manchuria? I don't want to be a downer, but by the time Manchuria becomes independent in 1911, Korea has lost its independence and is a non-autonomous province of Japan. They will not be doing anything whatsoever. Korea's fate is not going to change simply because Manchuria has a bit more land.
What will change about Korea though, is that when it reclaims its sovereignty from Japan, it will do so fully united. Unless Manchuria goes communist or stuff like that, there will be no one to directly back up the Kims in the Korean War when South Korea is whooping their ass. And even if Manchuria does turn communist and intervenes militarily, they'll be unlikely to turn the tide like China did. Manchuria may have heavily modernized by then, but I'm doubtful of their ability to push the Americans back over the borders.
excellent point in general, and counterpoint to the Korean lebensraum wank scenario concept
I honestly think Japan and Manchuria would moreso be allies. Manchuria, especially with Outer Manchuria, would be a joint buffer state against both China and Russia. Annexing or militarily occupying the region would give Japan a direct border with both. This strikes me as undesirable in a situation where Manchuria is already fully independent and does not require the presence of the Japanese military to even exist, especially considering that Manchuria and Japan have many reasons to be friends here.
A very interesting divergent possibility I had not considered.
I do think that if you keep greater Manchuria under the Qing, that could plausibly lessen the geopolitical pressure on Korea. A country not under imminent threat of Russian occupation might well be less of a Japanese target.
It is always a possible outcome. But nothing about the lack of Russian threat *has* to make it so. Before feeling threatened by Russia, Japan felt threatened/bullied/disrespected by China during its self-strengthening movement in the 1880s, even though it was confident enough it could win in the middle 1890s. China, not Russia, was Japan's first competitor for Korea.
I'm really interested in what this whole situation (Vassal Korean Empire + sovereign Manchu buffer state) could mean for the Pacific War, should such a conflict even still happen.
It would be a whole different pathway, to a whole different ballgame, but I won't deny that *a* ballgame could happen that could have some superficial resemblances to our world's Pacific War, even though its origins and particulars would be quite different.
Of course, a Japan that just has mainland vassals and buffer states instead of conquests on the Asian mainland could have an imperialist/expansionist experience in the 20th century that is far less "supernova"-like than Showa Japan, and just be a longer-term persist colonial power, like a Portugal, Spain, Belgium in Asia and parts of the Pacific.