I hope I'm not missing something, but I think you've misunderstood the rather confusingly named 'East Pakistan', which simply is modern Bangladesh - East Pakistan and what is now Pakistan were not contiguous.

East Pakistan was created in 1947 as a result of the partition of Bengal, which roughly divided the province of Bengal along religious lines, with the Western and predominantly Hindu part going to India, and the Eastern and largely Muslim part going to the governance of Pakistan, although, as is to be expected, demographic contours did not conform entirely smoothly with the new lines on the map.

The refugee crisis was a direct result of the Pakistani military's response to the Bangladesh independence movement (which had been developing since the partition, with the Pakistani implementation of Urdu as the official language, despite more than half the population being ethnically Bengali, an early flashpoint), considered to be genocidal in nature, involving mass rape and killings by both the Pakistani army and Islamist militias.

The response of the Nixon-Kissinger administration to the crisis - namely support of Pakistan due to concerns over USSR-Indian relationships and the potential to entice China, an ally of Pakistan - led to the 'Blood telegram', an unprecedented schism between Archer Blood, consul general to East Pakistan/Bangladesh, and the US administration.

I am certainly interested in the second aspect of your question, and also wonder the extent to which the political life of the Bangladeshi liberation movement was intertwined with Bengali politics as well as how the religious aspect played along ethnic lines, as Bangladeshi Bengalis were still Muslim.

I'm not knowledgeable on Pakistan/Indian history to answer your question in detail, but I believe that from how you've formulated your question there is a geographical misunderstanding here. I'm not sure though as you seem to be reading a book on the issue which would imply you know, so sorry if I'm being a presumptuous! Anyways, if that isn't the case feel free to point it out and I can remove my comment.

India was partitioned into three sections (essentially) in 1947, but under the two states of India and Pakistan. You had Pakistan in the West, India in the middle and East Pakistan in the East (also known as East Bengal, under Pakistani rule). Roughly 2200 kilometers separated East Pakistan from Pakistan proper (Edit: For reference, here is a map of Pakistan in 1971).

In 1971, Bangladeshis waged an independence war. Pakistan didn't drive Bengalis 2000 miles away, it was more that the war effort displaced millions of people in East Pakistan. Bengalis are from the region of Bengal, with the coastline being the Bay of Bengal - which is on the East coast of India, South coast of Bangladesh and West coast of Myanmar. At the time, East Bengal was in East Pakistan, and West Bengal was in East India.

As for the repercussions and so on - I can't tell you anything about that, sorry.

Since the other comments have not yet touched on this, I can try to address your final question of whether the events that led to Bangladesh’s independence are still salient today.

Without breaking the 20-year-rule, I can at least observe that two major political parties in Bangladesh derived their most influential members from the independence movement: Sheikh Mujib Rahman, who was elected in the ill-fated general elections of 1970, was leader of the Awami League; General Ziaur Rahman was central to Bangladesh’s military success once the war began in 1971 and ended up founding the Bangladesh Nationalist Party. Neither Sheikh Mujib nor Zia survived their tenures in state leadership (Sheikh Mujib was prime minister when he was assassinated in a military coup in 1975, while Zia met the same fate as president in 1981), but their parties remained active and helped end the second period of military rule (1982-1990) to bring a democratic system of government back to the country. Close family members took up the mantle of party leadership: Sheikh Hasina (Mujib’s daughter) became and remains the leader of the Awami League, while Khaleda Zia (Zia’s wife) became and remains the leader of the BNP.

The argument could therefore be made that the independence movement and its societal consequences — the exodus of refugees, violence committed during the war, the history of Bengali collaborators who aided the Pakistani army — are deeply intertwined with the subsequent political development of Bangladesh; however, I don’t want to overstep the bounds of history to get into political analysis (but feel free to PM me if you’re still curious). David Lewis’s Bangladesh: Politics, Economy, and Civil Society is a good primer on the country: I used that book to cite another AskHistorians reply a few years ago about the struggle for independence.

You are absolutely right this was a misunderstanding on my part! I had used Wikipedia when I was originally trying to sort this out and on the page for East Pakistan it highlighted both modern day Pakistan and 1960s East Pakistan (the region you explained).

Follow up question- why was this region called East Pakistan? What is the history of the names of the regions of this part of the world?

Thank you for your answer!