The British conquest of Bengal began with the Battle of Plassey.

Explanation:
The British conquest of Bengal did not begin with a single battle, but rather through a series of events ad battles over a period of time. However, one significant battle often associated with the British conquest of Bengal is the Battle of Plassey, which took place on June 23, 1757.

In this battle, the British East India Company forces, led by Robert Clive, defeated the army of Siraj ud-Daulah, the Nawab of Bengal. The victory at Plassey gave the British East India Company control over Bengal and marked the beginning of British colonial rule in India.