Mukti Bahini used Guerrilla warfare tactics to fight against the Pakistan Army. India provided economic, military and diplomatic support to the Mukti Bahini, leading West Pakistan to launch Operation Chengiz Khan, a preemptive attack on the western border of India which started the Indo-Pakistani War of 1971. The operation also precipitated the 1971 Bangladesh genocide and caused roughly 10 million refugees to flee to India. Essentially Bengali intelligentsia, academics and Hindus were targeted for the harshest treatment, with significant indiscriminate killing taking place. These systematic killings enraged the Bengalis, who declared independence from Pakistan, to achieve the new state of Bangladesh.