As the East India Company grew in size so did its lust for power. The decline of the Mughal empire and the rise of regional provinces like Bengal, presented the Company an opportunity for political interference. In 1740, Nawab Alivardi Khan of Bengal became practically independent. In 1756, his death led to a power struggle between his widow Ghasiti Begum and grandson Siraj Ud Daulah who became the Nawab of Bengal.
The company's support for Ghasiti Begum earned it the wrath of Siraj. The Company also started fortifying the Fort William without the Nawab's permission. On 20th June 1756, Siraj attacked and took over Fort William. Many of the English prisoners, who were imprisoned in a tiny room, died. This is often portrayed as the Black Hole of Calcutta. Many believe that the incident has been greatly exaggerated to suit the purpose of the Company.
The Company Fights back
The company sent in relief troops from Fort St. George of the Madras headquarters. The troops led by Robert Clive and Admiral Watson retook Calcutta on 2nd January, 1757. The treaty of Alinagar was signed between the Nawab and the Company.
However Clive's military ambitions were on the ascendancy. His troops captured the French settlement of Chandernagore. He tempted Siraj's uncle Mir Jafar to ally with him in exchange for the Nawab's position. On 23rd June, 1757, the Company troops marched against Siraj. Betrayed by his own men Siraj was defeated in the Battle of Plassey, which is said to have lasted only a few hours. He was soon assassinated in his capital Murshidabad. From being traders, the Company turned kingmakers in Bengal and Mir Jafar was installed as the new Nawab. Clive got his pound of flesh from the Nawab in terms of 234,000 pounds and was awarded an annual salary of 30,000 pounds per year. This made him one of the richest Britons in the world. The company also secure rights over a large area south of Calcutta. Construction of a new Fort William was started and was completed in 16 years in 1773. These events led to the rise of Calcutta and the decline of Murshidabad.