While I agree the past shouldn't determine the future, it's rather short sighted to say that the victims of European colonialism should forget & forgive. That's the way they get you - by moving their borders every few hundred years, and then convincing the world "it's in the past, move on already."Don't be amazed; it's very simple. People can't be mad at things that happened a century ago. Russia is an ally today while Japan and the UK are antagonists to China. Fire does not burn without a continuous fuel supply, which the Japanese and British never fail to supply. Vengeance over the past is just an excuse.
Europeans and their descendants went from having ~10% of the territory of the world to ~50% through this process of repeated invasions. It's even more than that if we count their Indo-European ancestors. This should not be forgotten, nor should it be forgiven. A civilization/race expanding their territory this way is an existential threat to everyone else. It cannot be allowed to repeat.
Whether China ultimately takes back Siberia / Far East depends on Russia's behavior and alignment, but we must never forget or forgive European expansionism, which led to the extinction of native civilizations and races on three continents and a lasting legacy of cultural and ideological imperialism that persists to this day. The other peoples of the world deserve to live free from the threat of periodic European mass invasion / genocide. As a civilization, they must be contained.