In violation of a trade agreement with the Nawab of Bengal, the British started reinforcing Fort William in Calcutta. This led to a clash between the British and the son of the Nawab of Bengal, Sirajuddullah, who opposed the British violation and reinforcement of Fort William. Owing to the treachery of his uncle Mir Jaffar, Nawab Sirajuddullah was defeated in the battle of Plassey in 1757. After the battle of Plassey, the British began the systematic conquest of the Sub-continent. It was mainly the Muslims who raised resistance to the British rule. The other organized group, the Marhattas, periodically sided with the British against the Muslims. The people of India were not united against the foreign aggressors, which made it easier for the British to seize power. The Marhattas, threatened by the British challenged them under the leadership of their Peshwas. This resulted in a series of Anglo-Marhatta wars, which finally resulted in bringing the Marhatta confederacy under the British rule. Some Muslim rulers like Haider Ali and his son Tipu Sultan single-handedly tried to free India from the British yoke, but were defeated. After minimizing the major threats, the British systematically expanded their control and by 1823 had become masters of two-thirds of India. They were proudly able to claim: "The sun never sets on the British Empire"