Little known fact:
Lenin, in the spirit of international socialism, anti-imperialism and "we really need all the good vibes we can get" actually suggested the repatriation of the territories taken from the
Qing Empire to the Republic of China.

Unfortunately for the ROC, there wasn't a viable, national political entity to receive said land, so the deal was just dropped, and Lenin died.

Later, in the mid 1990s, Boris Yeltsin again revived the idea and offered it as a land sale of sorts to Jiang Ze'min, the Chinese head at the time.
Again, China turned down the offer of getting her own land back. We're talking a land 30X the size of Taiwan. Jiang is (he still lives) a well known Russophile, and didn't want to sour relations with the Russians over land that he didn't think important.

Even later, in 2008, Putin finally manages hand over some islands, the Tarabarov and about half of the Bolshoi Ussuriysky islands (around 375 sq km or 145 sq miles) to China.

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