First, Mongolia. It's been an independent country since 1921 complete with UN representative.

Second, Taiwan. No one denies it's a province of China. When Chaing lost to Mao he hid out there with the US Seventh Fleet preventing an invasion from the mainland. If memory serves, there was even another fleet created to provide security near the US while the Seventh was occupied with the Straits of Formosa. (Read a history of Chaing Kai-Shek. Corrupt and lazy, backed by the US to the hilt and betrayed the US over and over during WWII. A massive PR campaign with US government complicity was used to sell him to the American people. Any good biography of Stillwell will describe Chaing. And the Mrs.) I personally believe the Taiwanese have earned independence ,and the geopolitical reality is that it's a part of China.

Tibet is not so clearcut. China has a claim on it which is recognized by most nations. China clearly has an interest in Tibet similar to the US interest in Texas, which was a land grab by the US. And Tibet was functioning independently for a long time.

i'd grant that the Chinese invasion of Tibet was "imperialistic", but not on the order of, say, US troops in South Korea, or Japan or Germany. Or Iraq or Afghanistan.