1. Battle of Buxar ((Oct. 22, 1764) Background
Battle of Buxar a conflict between forces of the British East India Company, commanded by Major Hector Munro, and those of the Mughal emperor, Shah Alam II; the Mughal governor of Oudh Shujā al-Dawlah; and the governor of Bengal, Mīr Qāsim.
Causes
Mir Kasim was the most efficient of all Nawabs of Bengal from 1756 onward
By keeping himself away from the British influence. For that purpose he transferred his capital from Murshidabad to Monghyr.
To strengthen his power he organized his army in the same way as the Europeans did.
He made arrangements for the manufacture of fire arms at Monghyr with a view to equipping his army adequately

2. 5. Mir Kasim wanted to put an end to all private trade.
6. Under instructions, from the Nawab, his officers in the district began to seize the boats belonging to the English merchants
7. He also instructed the local Amils to strike off all kinds of commercial relations with the East India Company. All these measures led to huge financial loss to the company.
8. He fled to get the assistance from Oudh Shuja-ud-daula, the Nawab of Oudh, and the Mughal Emperor Shah Alam. These three people formed a confederacy against the British.
Course of War
Their combined army met the British forces under the command of Major Munro at Buxar on 22nd October 1764.
Major Munro inflicted a crushing defeat on their combined forces.
Mir Kasim fled to the North-West and died.
Shah Alam left the cause of Shuja-ud-daula and found shelter in the British camp.
Shuja-ud-daula fought until 1765 when he was completely defeated and sued for peace.

3. Treaty of Allahabad:
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.
The Battle of Buxar firmly established the British as masters of Bengal, Bihar and Orissa and placed Awadh at their mercy.