The Qing were originally Manchu invaders.
And yes, the Qing empire is still viewed by many in China to be illegitimate.
Tens of millions of Chinese died during the Manchu invasion of China. The Qing forced every Han Chinese male to shave their forehead and wear a queue on the threat of death, but that's apparently not humiliating.
When the Mongols and Manchu conquered the Chinese "Crown" it was more of a change of dynasty and they they effectively became Chinese. Mongolia was part of the Chinese empire until its fall in 1912, for instance.
But in England and the West in general, China found an adversary that could defeat them militarily, and which had no interest in adopting their culture or civilization. Quite the contrary, the new foreign invaders were disrepectful of Chinese culture in a way that was new and shocking.