The main cause of the conflict between Nawab Sirajuddaulah and the East India Company was that the British attacked the French settlement of Chandranagar in Bengal. This event played a significant role in escalating tensions between the Nawab and the British.

The British Attack on Chandranagar:
The British attack on Chandranagar, a French settlement in Bengal, was a crucial factor that led to the conflict between Nawab Sirajuddaulah and the East India Company. The British saw the French as a potential threat to their expanding power in India and aimed to eliminate their influence. In 1756, the British launched an attack on Chandranagar, which was under the control of the French. This attack was seen as a direct challenge to the Nawab's authority as the ruler of Bengal.

Impact on Nawab Sirajuddaulah:
The attack on Chandranagar deeply angered Nawab Sirajuddaulah. He felt that the British had violated his sovereignty and disregarded his authority. This event marked a turning point in his relationship with the East India Company, as he became increasingly distrustful of their intentions and actions.

Loss of Trade Concessions:
As a result of the attack on Chandranagar, the Nawab came to believe that the British misused the trade concessions granted to them. The East India Company had been given certain privileges by previous Nawabs, including the right to trade in Bengal. However, Sirajuddaulah felt that the British had overstepped their boundaries and used these concessions to further their own interests, rather than engaging in fair trade.

Growing Tensions:
The attack on Chandranagar and the perceived misuse of trade concessions by the British created a deep sense of resentment and mistrust between Nawab Sirajuddaulah and the East India Company. The Nawab became determined to assert his authority and protect the interests of his kingdom. This ultimately led to the Battle of Plassey in 1757, where Sirajuddaulah was defeated by the British forces, marking the beginning of British domination in Bengal.

In conclusion, the attack on the French settlement of Chandranagar by the British was the main cause of the conflict between Nawab Sirajuddaulah and the East India Company. This event deeply angered the Nawab and led to his growing mistrust of the British, as he believed they had violated his sovereignty and misused their trade concessions. These tensions eventually culminated in the Battle of Plassey and the subsequent British domination in Bengal.