The Jamaat never supported the Muslim League before 1947 during the struggle for independence from the British. The Jamaat opposed the Muslim league's demand for a home land for the Muslims in India. However once Pakistan came into existence they started to campaign for political power in the new state by demanding the introduction of Islamic Law the contents of which would be defined by their theologians. Pakistan had two wings, the west wing which alone constitutes present day Pakistan and an east wing, East Bengal in undivided India, which attained sovereignty in 1971 after a war of liberation against the western wing. The new state was Bangladesh.
All wars are brutal.
This was particularly so because of the political use of religion to marshal forces against the Bengalis. The Pakistani army was mobilised against the citizens of East Pakistan. The Jamaat not only collaborated with the army but they were directly responsible for many atrocities. They were thus totally discredited when Bangladesh became independent. This experience crystallised the determination in Bangladesh never to allow religion to be used for political purposes and secularism was written in as a fundamental principle of the new Constitution.