Historically China and the northern empires, whether they are Xiongnu, Liao, Jin, Mongol or Russian, would fight over the borders and the border often moves around due to waning and waxing of empires. The border area of Mobei and Outer Manchuria is desolate. Very few people live here, it was historically a buffer zone between rich China proper and rich central Asia. China first conquered it from Russia
, Russia conquered it back
, shit happens. The current border is the most of Manchuria that China has ever gotten except for the period from 1689-1858. It is hard to get emotional over this, which is why people don't get emotional over it, and the idea never gets popular support.
According to the
, Japan was to have returned all lands annexed by the Empire of Japan. Yet today Okinawa and Diaoyu Island are still occupied by Japan and they're still supporting Taiwanese independence. UK handed back their concessions because they knew they had no chance of holding it, but still set harmful traps in them.
UK and Japan are continuing to harm China today. If they stopped harming China, people would only regard their imperialism as historical, rather than ongoing.