The East India Co. – Battle of Buxar,1764 and full control over Bengal

At the outset the East India Company's main aim was not to rule India, but to make money by way of trading. Taxes were collected for them by a Company - appointed deputy - nawab.
After Robert Clive's diabolical victory in the Battle of Plassey in 1757, the puppet government of a new Nawab of Bengal - Mir Jaffer , was maintained by the East India Company. However, after the invasion of Bengal by the Nawob of Oudh in 1764 and his subsequent defeat in the Battle of Buxar,Bengal on October 23,1764 which was fought by East India company led by Hector Monroe agianst combined Mughal rulers of Mir Qasim, the Nawab of Bengal, Shuja-ud-Daulah the Nawab of Awadh, and the Mughal King Shah Alam II, the Company obtained the Diwani rights (revenue authority) over 100,000, 000 acres (400,000.00 sq. km) - treaty of Allahabad - which included the rights to administer and collect land-revenue (land tax) in Bengal, the region of present-day Bangladesh, West Bengal, Bihar, Jharkhand and U.P. Shah Allam was forced to pay a fine of five million rupees. After negotiation, the Treaty of Allalabad was signed. All his pre-war possessions were returned except for the districts of Karra and Allahabad. He became a pensioner, with a monthly pension of 450,000.00 rupees. Nawab Shuja-ud-Daula was restored to Oudh, with a subsidiary force and a guarantee of defence. Mir Qasim, the (puppet) Nawab of Bengal, was ruined by the defeat and later he was deposed by the company. In 1772, the Company also obtained the Nizāmat of Bengal (the "exercise of criminal jurisdiction") and thereby full sovereignty of the expanded Bengal Presidency. During the period, 1773 to 1785, very little changed; the only exceptions were the addition of the dominions of the Raja of Banares to the western boundary of the Bengal Presidency, and the addition of Salsette Island to the Bombay Presidency.
The East India company became a Mughul revenue agent for Bengal and later Bihar and by 1793 company's control was virtual.
In short the scheming British subsequently through a web of intrigues, betrayal and espionage reduced once prosperous Indian Maharajas and Nawobs to panhandlers seeking alms (pensions) from them and they never felt ashamed of their lousy treatment of Indian rulers who were once cooperative and hospitable to them when they opened up trading posts in various parts of India.

A Dictionary of Modern History (1707 - 1947), Parshotam Mehra, ISBN 9780195615524, 1985 ed., Oxford University Press