A couple interesting videos on Bangladesh to get started – first a look at Bangladesh’s independence in 1971, and how it is an extremely rare case of unilateral secession that was accepted by the wider global community. Independence movements try to secede unilaterally all the time (that is, break away against the wishes of the parent country), but since WWII, that rarely leads to acceptance as your own country by the UN or the wider global community.
India and Bangladesh used to share the messiest and most complicated border, with enclaves, second-level enclaves, and even a third-level enclave (a piece of India, surrounded by a piece of Bangladesh, which is surrounded by a piece of India, which is surrounded by Bangladesh). These borders were cleaned up recently, and but why they happened in the first place, and why it took so long to fix is up to both pre-Raj history, and India’s disputes with countries other than Bangladesh.
Bangladesh is one of the most populous Muslim countries, at around 150 million Muslims (90% of the country’s population, and Bangladesh makes up about 10% of the world’s Muslims). Bengal was a heavily Muslim region long before Partition, and the video below covers the spread of Islam into the subcontinent, the establishment of the Sultanate of Bengal, and Bengal’s incorporation into the Mughal Empire. It’s a good bird’s eye view of pre-British history.