The 1971 India-Pakistan War was a major military conflict between India and Pakistan that led to the creation of Bangladesh. It officially began on December 3, 1971—when Pakistan launched Operation Chengiz Khan, a series of air strikes targeting air bases in northwestern India. India had already been supporting the Bangladesh liberation movement for months, including providing training, arms, and assistance to Mukti Bahini guerrillas. India retaliated to Operation Chengiz Khan by declaring war and launching a large-scale ground invasion of East Pakistan.