Direct Action Day, also known as the Great Calcutta Riot, was on 16 August 1946—a day of widespread riot and manslaughter in the city of Calcutta (now known as Kolkata) in the Bengal province of British India. The day also marked the start of what is known as "The Week of the Long Knives".
The Muslim League and the Indian National Congress were the two largest political parties in the Constituent Assembly of India in the 1940s. The 1946 Cabinet Mission to India for planning of the transfer of power from the British Raj to the Indian leadership proposed an initial plan of composition of the new Dominion of India and its government. However, soon an alternative plan to divide the British Raj into a Hindu-majority India and a Muslim-majority Pakistan was proposed. The Congress rejected the alternative proposal outright. Muslim League planned general strike (hartal) on 16 August to protest this rejection, and to assert its demand for a separate Muslim homeland.
The protest triggered massive riots in Calcutta, instigated by the Muslim League and its Volunteer Corps against Hindus and Sikhs, followed by retaliatory attacks on Muslims by Congress followers and supporters. In Calcutta, within 72 hours, more than 4,000 people lost their lives and 100,000 residents in the city of Calcutta were left homeless. Violence in Calcutta sparked off further religious riots in the surrounding regions of Noakhali, Bihar, United Province (modern Uttar Pradesh), Punjab, and the North Western Frontier Province. These events sowed the seeds for the eventual Partition of India.
August 16 would be observed by the Muslim League as "the Direct Action Day". On that day Calcutta witnessed a communal riot, the scale and intensity of which had never been known in living memory. "The Great Calcutta Killing" touched off a chain reaction of violent communal explosions in East Bengal, Bihar and the Punjab,
As the news of disturbances in Bengal came through, Gandhi cancelled all his plans and decided to leave for the riot-affected areas. In East Bengal he noticed how fear, hatred and violence had come to pervade the countryside. He toured the villages, saw things at first hand, and tried to lift the issue of peace from the plane of politics to that of humanity. Whatever the political map of the future, he pleaded, it should be common ground among all parties that standards of civilized life would not be thrown overboard.