The scenario describes the partition of India in 1947, which led to the displacement of around 17 million individuals. This event was primarily driven by political reasons, specifically the division of British India into two independent dominions, India and Pakistan, based on religious lines (Hindus and Muslims).
Given this context, the most appropriate response regarding the reason for migration is:
forced political migration
This type of migration occurs when individuals are compelled to move due to political changes, upheaval, conflict, or oppression, which accurately reflects the circumstances surrounding the partition. The displacement was not voluntary; it was a consequence of the political decisions made during the partition.