Sentiments of Indian nationalism were expressed as early as 1885 at the Indian National Congress, which was predominantly Hindu. In 1906 the All-India Muslim League formed with favorable relations towards British rule, but by 1913 that changed when the League shifted its focus and began to view Indian self-government as its goal. It continued to favor Hindu-Muslim unity towards that end for several decades but in 1940 the League began to call for a separate Muslim state from the projected independent India. The league was concerned that a united independent India would be dominated by Hindus. In the winter of 1945-46 Mohammed Ali Jinnah's Muslim League members won all thirty seats reserved for Muslims in the Central Legislative Assembly and most of the reserved provincial seats as well.
In an effort to resolve deadlock between Congress and the Muslim League in order to transfer British power "to a single Indian administration", a three-man Cabinet Mission formed in 1946 which drafted plans for a "three-tier federation for India." According to those plans, the region would be divided into three groups of provinces, with Group A including the Hindu-populated provinces that would eventually comprise the majority of the independent India. Groups B and C were comprised of largely Muslim-populated provinces. Each group would be governed separately with a great degree of autonomy except for the handling of "foreign affairs, communications, defense, and only those finances required for such nationwide matters." These issues would be addressed by a minimal central government located in Dehli.
The plan, however, did not take into account the fate of a large Sikh population living in Punjab, part of the B-group of provinces. Mughal emperors' persecution of Sikh gurus in the 17th century had infused the Sikh culture with a lasting anti-Muslim element that promised to erupt if the Punjab Sikhs were to be partitioned off as part of a Muslim-dominated province group. Although they did not make up more than two per cent of the Indian population, the Sikhs had since 1942 been moving for a separate Azad Punjab of their own, and by 1946 they were demanding a free Sikh nation-state.
As leader of the Muslim League, Jinnah accepted the Cabinet Mission's proposal. However, when Nehru announced at his first press conference as the reelected president of Congress that "no constituent assembly could be bound by any prearranged constitutional formula," Jinnah took this to be a repudiation of the plan, which was necessarily a case of all or nothing. The Muslim Leagueís Working Committee withdrew its consent and called upon the Muslim nation to launch direct action in mid-August 1946. A frenzy of rioting between Hindus and Muslims ensued.
In March of 1947 Lord Mountbatten was sent to take over the viceroy, and encountered a situation in which he feared a forced evacuation of British troops. He recommended a partition of Punjab and Bengal in the face of raging civil war. Gandhi was very opposed to the idea of partition, and urged Mountbatten to offer Jinnah leadership of a united India instead of the creation of a separate Muslim state. However, Nehru would not agree to that suggestion. In July Britain's Parliament passed the Indian Independence Act, which set a deadline of midnight on August 14-15, 1947 for "demarcation of the dominions of India." As a result, at least 10 million Hindus, Muslims and Sikhs fled their homes to seek sanctuary on whichever side of the line was favorable to them. The ensuing communal massacres left at least one million dead, with the brunt of the suffering borne by the Sikhs who had been caught in the middle. Most of them eventually settled in Punjab.
Jinnah presided as the governor-general of Pakistan, which was geographically divided into East Pakistan and West Pakistan and separated by Indian territory (including half of Punjab and half of Bengal). However, ownership of Kashmir remained in dispute until it came to a head and war broke out once again in 1965. The unrest did not end there; in 1971 tensions between East and West Pakistan over Bengali autonomy developed into another civil war, with the result that Bangladesh became an independent country in 1972 and West Pakistan remained Pakistan.
Source: Encyclopedia Britannica online