What caused the Sino-Indian War?

The reason is that Indian Prime Minister Nehru overreached himself, claiming to be a big country, and attempted to occupy about 92,000 square kilometers of land south of the McMahon line in southern Tibet as the successor of the British colonists, and openly occupied our territory. Our army then committed the crime of annihilating all the Indian troops in Aksai Chin area in southern Xinjiang and Tawang area in southern Tibet respectively, but later I don't know why I took the initiative to retreat for 20 kilometers (some people said that it was because our army could not supply logistics, but it was not. At that time, our army had enough food and grass to cope with it for more than a month, which led to 92,000 square kilometers in southern Tibet falling into the hands of Indian Asan for more than 47 years. Now India has immigrated more than 5 million people here in an attempt to create a fait accompli. India calls Tawang and other places "Anunnachar State". Because this land is located at the southern foot of the Himalayas, with low terrain (only 1000m-2000m above sea level) and humid climate, it is a famous "land of rice" in Tibet.