The Radcliffe Line, a border between the Union of India and the Dominion of Pakistan, was unveiled on August 17, 1947.

The Radcliffe Line, a border between the Union of India and the Dominion of Pakistan, was unveiled on August 17, 1947.

Following India's partition on August 17, 1947, the Radcliffe Line was proclaimed as the border between India and Pakistan. The line is named after Sir Cyril Radcliffe, who was tasked with dividing 4,50,000 square kilometers of land among 88 million people.

The Radcliffe Line was designed to divide India along religious demographic lines, with Muslim-majority provinces becoming part of the new nation of Pakistan and Hindu and Sikh-majority provinces remaining in India.

The Indian Independence Act 1947 of the United Kingdom Parliament, which went into effect on July 15, 1947, stipulated that India would be free of British dominion on August 15, 1947, exactly a month later. The act also agreed to divide British India's provinces into two new states, the Union of India and the Dominion of Pakistan (which would be further divided into the Islamic Republic of Pakistan and the People's Republic of Bangladesh). Pakistan was meant to be a home for Indian Muslims, whereas India, with a Hindu majority, was supposed to be a secular state.

Before Partition, princely states covered 40% of India, which were not British colonies and so did not form part of British India. As a result, the British were unable to grant them independence or split them. As a result, the rulers of these states were entirely sovereign and had to select which of the two nations they wished to join (or remain independent). However, all of the monarchs quickly elected to join India or Pakistan, with only a few exceptions.

Because India was partitioned based on religious demographics, Muslim-dominated regions in northern India were to become part of Pakistan. Baluchistan and Sindh (both of which have a strong Muslim majority) were automatically incorporated into Pakistan. The issue lay in the two provinces of Punjab (55.7% Muslim) and Bengal (54.4% Muslim), which did not have a large Muslim population. The western portion of Punjab eventually became part of West Pakistan, while the eastern section became part of India (the eastern part of Punjab was later partitioned into three additional Indian states). The state of Bengal was also divided, with East Bengal becoming part of Pakistan and West Bengal remaining in India. Following independence, the North West Frontier Province (near Afghanistan) decided to join Pakistan.

Because Punjab's population was dispersed, it was impossible to create a line that separated Hindus, Muslims, and Sikhs. Similarly, neither the Muslim League, led by Jinnah, nor the Congress, led by Nehru and Sardar Patel, supported any boundary formed. As a result, it was agreed what was needed was a well-drawn line that would limit the separation of farmers from their fields while also minimizing the number of people who would have to relocate, so diminishing the feeling of alienation that a new place provides. 

Lord Wavell, the Viceroy of India, had drawn a rough border before being replaced by Lord Mountbatten in February 1947. In June 1947, Britain appointed Sir Cyril Radcliffe to head the two Boundary Commissions (one for Punjab and one for Bengal) to determine which regions would be given to which nation. The Boundary Commission was tasked with demarcating districts in Punjab based on religious majority. While defining the boundary, Radcliffe considered "natural boundaries, communications, watercourses, and irrigation systems," as well as socio-political issues. Each Boundary Commission comprised four representatives, two from the Congress and two from the Muslim League, and given the antagonism between the two, the decision on the boundary ultimately rested with Radcliffe.

Radcliffe landed in India on July 8, 1947, and was assigned to serve on the border for five weeks. Following his meeting with Mountbatten, Radcliffe traveled to Lahore and Kolkata to meet his Boundary Commission colleagues, who included Jawaharlal Nehru of the Congress and Muhammad Ali Jinnah of the Muslim League. Both parties wanted the line finalized by August 15, 1947, in time for the British to leave India. Radcliffe finalized the boundary line a few days before Independence, as desired by both Nehru and Jinnah, but for political considerations, the Radcliffe Line was only formally unveiled on August 17, 1947, two days after Independence.