Basically East Pakistan ( now Bangladesh ) wanted independence from Pakistan. Which led to the Pakistani military committing genocide with deaths estimated from 300k - 3 million

Eventually war breaks out with a Pakistani preemptive strike on Indian airfields. The war lasts around two weeks with an Indian/Bangladeshi victory. Around 8-10 million refugees went to India.

The US supported Pakistan and did not want India to intervene. Mainly because India had good relations with the USSR I suppose. The USSR supported India and Bangladeshi Independence and would support India against the US and China

So during the war the US sends in a carrier group to the Indian Ocean to send a message, which was countered by the USSR sending their navy. Nixon tried to get China to send troops to the Indian border but they did not agree. China had defeated India recently in the 1962 and supported Pakistan.

So there are many ways things could’ve gone differently. What if China and the US did enter the war, or just one of them? What if the the USSR was neutral here? I want to read a lot more about this time period