The partition was set forth in the Indian Independence Act 1947 and resulted in the dissolution of the British Raj, as the British government there was called. The two self-governing countries of Pakistan and India legally came into existence at midnight on 14–15 August 1947.

Partition” – the division of British India into the two separate states of India and Pakistan on August 14-15, 1947 – was the “last-minute” mechanism by which the British were able to secure agreement over how independence would take place. At the time, few people understood what Partition would entail or what its results would be, and the migration on the enormous scale that followed took the vast majority of contemporaries by surprise.

The main vehicle for nationalist activity was the Indian National Congress, whose best-known leaders included Mahatma Gandhi and Jawaharlal Nehru. Even before the 1940s, it had long argued for a unitary state with a strong centre; even though Congress was ostensibly secular in its objectives, organisations representing minority interests increasingly viewed this idea with suspicion, believing that it would entrench the political dominance of Hindus, who made up about 80% of the population.

At around 25% of its population, Muslims were British India’s largest religious minority. Under imperial rule, they had grown accustomed to having their minority status protected by a system of reserved legislative seats and separate electorates. The British system of political control hinged on identifying interest groups willing to collaborate, a governing style often described as “divide and rule”.

The partition occurred due to religious beliefs .The Muslim league demanded for two nation theory in which they said that india is a part of two communities that is Muslim and Hindus ..so the country should be divided into two country one of Hindi beliefs and other of Muslims .although Indian govt was opposed to this theory but at the end the Muslim league was is majority so they finally divided the country into two beliefs .Thus the Hindi speaking remained in India and the Muslims in pakistan [M.A Jinnah was also of Muslim league ] point to be noted ! I hope that this will help you!