This to me has always been one of those very visible signs (not certainties but signs in my opinion) of how nuclear weapons have changed the conduct of large nations.

At most times in history before the advent of nukes, a geographical/political situation of a hugely populated major power being right below the vast, sparsely populated but resource rich territory of another large nation with a tenth the population would have absolutely resulted in a war of conquest and annexation by the former. Now it simply doesn't, partly no doubt because of international laws around wars of aggression and threats of international condemnation or economic sanction, but mostly I suspect just because the weaker power happens to be almost uniquely strong on having a shitload of nukes with which it can annihilate the other country regardless of the size of the latter's population, armies and economy.

Before the 1940's Russia had no nukes and the two were in the same geographical situation, but China was then extremely weak, unlike now. Today's economic and political situation between the two translated to a pre-nuclear world would be very different I think.

In theory, Ukraine has a agreement with China that China would protect Ukraine from nuclear threats ( supposedly through the one road one belt agreement).

http://america.aljazeera.com/articles/2014/3/7/china-s-unusu...

They also are turning against Ukraine, although they mentioned something different in the past:

> The Chinese Government has constantly opposed the practice of exerting political, economic or other pressure in international relations. It maintains that disputes and differences should be settled peacefully through consultations on an equal footing. Abiding by the spirit of the Sino-Ukrainian joint communiqué of January 4, 1992 on the establishment of diplomatic relations, the Sino-Ukrainian joint communiqué of October 31, 1992 and the Sino-Ukrainian joint statement of September 6, 1994, China recognizes and respects the independence, sovereignty and territorial integrity of Ukraine, and stands ready to further develop friendly and cooperative Sino-Ukraine relations on the basis of the Five Principles of Peaceful Coexistence.

https://en.wikipedia.org/wiki/Nuclear_weapons_and_Ukraine#Fr...

It of course would only happen if the current regime were to fall. Perhaps 'annex' is too hard a word. Maybe 'cover all oustanding debts and throw in some lucrative personal deals for the current Kremlin warlord'?

Napoleon sold a large chunk of North America for "$11.25 million, plus the forgiveness of $3.75 million in French debt".

https://www.history.com/news/8-things-you-may-not-know-about...