The Battle of Plassey

On June 23, 1757 AD, the Battle of Plassey took place in Bengal between the forces of Nawab Mirza Mohammad Siraj od-Dowlah and the British, who with the help traitors like Mir Ja’far, Rai Durlabh and Omichand, defeated the demoralized Indian forces. The young Siraj od-Dowlah, who was of Iranian origin was caught and executed, while fleeing. Robert Clive, the commander of the British forces, installed Mir Ja’far – also of Iranian origin – as the new Nawab of Bengal, after extracting huge concessions from him. With this battle the British established their foothold in India and would over the next half-century century take complete control of the Subcontinent.

British false propaganda about the "Black Hole of Calcutta"
On June 20, 1756 AD, with the fall of the British garrison of Fort William to Mirza Mohammad Siraj od-Dowla the 18-year old Nawab of Bengal, Bihar and Orissa, John Zephaniah Holwell coined the myth of the "Black Hole of Calcutta" to tarnish the image of the Indian people by alleging that 146 Englishmen were crammed in a 14 by 18 feet (4.3 أ— 5.5 m) dungeon that resulted in the death of 123 of them. Holwell, who claimed to be a survivor, has long been disproved by historians and researchers. R.C. Majumdar in his book "An Advanced History of India" has dismissed the Black Hole story as entirely baseless.
British scholar J.H. Little in his article, titled "The 'Black Hole'—The Question of Holwell's Veracity", argues that Holwell's version is nothing but "a gigantic hoax" – invented to rouse sentiments in Britain for military intervention in India. Fort William was set up to protect the British East India Company's trade in Bengal from its European rivals, the French and the Dutch. Siraj od-Dowlah, who was the local ruler of Iranian origin, objected to British meddling in the affairs of his dominion, perceiving the militarization of Fort William as a threat to its independence. He ordered an immediate stop to military enhancement and when the British paid no heed, he laid siege and seized the fort. In 1757, the British sent an army under Robert Clive and by bribing officers of Bengal including the Prime Minister, defeated Siraj od-Dawla in the Battle of Plassey.