Encyclopedia Britannica
In March 1959 a revolt erupted in Lhasa, the capital of Tibet, which had been under the effective control of the People’s Republic of China since 1951.
The uprising occurred amid general Tibetan fears that the Chinese government might arrest the 14th Dalai Lama.
14th Dalai Lama 1959 – Wikipedia
Clashes quickly became violent and the Chinese People’s Liberation Army (PLA) used force to put them down..
In its last stages, the uprising included heavy fighting, with high civilian and military losses. Thousands were killed although the exact number is disputed.
The 14th Dalai Lama escaped from Lhasa, while the city was fully retaken by Chinese security forces on 23 March 1959.
Source; Wikipedia