The Battle of Buxar was a decisive battle fought between British and Indian forces at Buxar, a town on the Ganges River.
Mir Kasim, the Nawab of Bengal, wanted to rid his territory of British control. He formed an alliance with the Nawab of Oudh and Shah Alam II, the Mughal emperor. The combined Indian armies invaded Bengal and clashed with British troops, led by Major Hector Munro, in October 1764. A hotly contested battle resulted in victory for the British.
As a result of this triumph, in 1765, Robert Clive signed the Treaty of Allahabad with the Nawab of Oudh and Shah Alam II. The treaty effectively legalized the British East India Company’s control over the whole of Bengal.
Shuja was restored to Awadh, with a subsidiary force and guarantee of defence, Emperor Shah Alam solaced with Allahabad and a tribute and the frontier drawn at the boundary of Bihar. In Bengal itself he took a decisive step. In return for restoring Shah Alam to Allahabad he received the imperial grant of the diwani or revenue authority in Bengal and Bihar to the Company. This had been enjoyed by the nawab, so that now there was a double government, the Nawab retaining judicial and police functions, the Company exercising the revenue power.
This arrangement made the Company the virtual ruler of Bengal since it already possessed decisive military power. All that was left to the nawab was the control of the judicial administration.