Battle of Plassey (1757): Misinterpretation of the Mughal firman granted to the British in 1717 and the misuse of Dastaks (free passes) became the source of constant tension between the Bengal Nawabs and EIC. Siraj-ud-daulah the young Nawab of Bengal wanted the company to work under certain restrictions but after their success in south India, the EIC became too bold to obey the Nawab. Against the orders of the Nawab, the British fortified Calcutta against future French attack. Siraj-ud-daulah captured the English factory at Kasim Bazar and thereafter took control of Fort William. The English prisoners were confined in a small room known as Black Hole.
It is alleged that in this small room 123 Englishmen died of suffocation. After the fall of Calcutta, the English took refuge at Fulta. A strong army and naval force under Clive and Admiral Watson was dispatched to Calcutta. Manikchand who was given charge of Calcutta by Siraj-ud-daulah deserted the city and allowed the British to capture Calcutta again. The Nawab concluded the treaty of Alinagar on 9th February, 1757 and conceded all the British demands. In violation of the Alinagar treaty, the British captured Chandarnagar in March 1757. Now, the British wanted to replace Siraj-ud-daulah by Mir Jafar. Mir Jafar, Rai Durlabh the two generals of the Nawab and Jagat Seth, a rich banker of Calcutta joined a conspiracy against the Nawab. The battle of Plassey was fought on 23rd June, 1757. Mir Jafar and Rai Durlabh hardly fought. Only a small force under Mohan Lal and Mir Madan took part in the battle. The British forces easily defeated the Nawab.
Importance of the Battle of Plassey: It paved the way for British control over Bengal and later the whole of India. The British now, became a major power to replace the Mughal rule in India. The company amassed huge wealth from Bengal.
Battle of Buxar (1764): Even Mir Jafar was not able to keep the greed of the British satisfied. The British removed him and made Mir Qasim the new Nawab of Bengal. After some time, even Mir Qasim began to oppose the British sovereignty over him. He was joined by Shuja-ud-daulah of Awadh and Shah Alam II, the Mughal emperor in the battle of Buxar on October 22, 1764 against the British. This time, the British Army led by Hector Munroe defeated the three most powerful combined forces of India.
Importance of the Battle of Buxar: The British became the rulers of Bengal, Bihar and Orissa. The Nawab of Awadh became dependent on the company and the Mughal emperor became a pensioner of the company.