> People remember.
No. People don't remember over a sufficiently long period of time.
For instance, you mention China, Russia and the British Empire, but if you look further in time, you get to see other things which nobody remembers:
> The Islamization of Xinjiang started around 1000 AD by eliminating Buddhism. [1].
> Many Buddhists fear that their countries will lose their culture and become Muslim, as had been the case in many parts of modern day Central Asia, Xinjiang, Afghanistan, and Pakistan, which were majority Buddhist before the arrival of Islam in the 7th-11th centuries. [...] When the Muslim Turkic Qarakhanids captured the Buddhist city of Khotan in Xinjiang in 1006 CE, one of their poets penned this verse: “We came down on them like a flood/We went out among their cities/We tore down the idol-temples/We shat on the Buddha’s head.” In the Islamic world, a destroyer of idols came to be known as a but-shikan (بت شکن), a destroyer of but, a corruption of the word Buddha. [2]
Long before the Islamization of Buddhist Uyghur, there were "Caucasoid" people, which would be impossible to know without the discovery of the Tarim "Celtic" mummies (~2000 years BC) [3].
> From the evidence available, we have found that during the first 1,000 years after the Loulan Beauty [~4000 years ago], the only settlers in the Tarim Basin were Caucasoid. East Asian peoples only began showing up in the eastern portions of the Tarim Basin about 3,000 years ago, Mair said, while the Uighur peoples arrived after the collapse of the Orkon Uighur Kingdom, largely based in modern day Mongolia, around the year 842. [4]
[1] https://en.wikipedia.org/wiki/Xinjiang#Demographics
[2] https://thediplomat.com/2017/10/buddhism-and-islam-in-asia-a...
[3] https://en.wikipedia.org/wiki/Tarim_mummies
[4] https://www.independent.co.uk/news/world/asia/meeting-civili...