The main cause for starting the Quit India Movement in 1942 was the failure of the Cripps Mission. The Cripps Mission was a British initiative aimed at discussing India`s future political framework. However, the proposals made by the mission were rejected by both the Indian National Congress and the Muslim League. This failure led to a sense of frustration among the Indian population, as they felt that their demands for self-governance were being ignored by the British government. As a result, the Quit India Movement was launched, calling for the immediate withdrawal of British colonial rule from India. This movement gained widespread support and marked a significant turning point in the Indian freedom struggle.