Mir Jafar chafed at the interference of Clive, but he could hardly dispense with the military help of the English. This was strikingly illustrated when, in 1759, Shah Alam II planned, to occupy Bengal and Bihar and laid siege to Patna. Jafar succeeded in averting this danger with the help of Clive, but the episode was a rude reminder to him, if any such were necessary, that however unwelcome the English might be, their help was essential to keep himself on the throne. Finally, Mir Jafar tried the desperate expedient of changing one master for another and entered into a conspiracy with the Dutch at Chinsura. The Dutch were very eager to supplant the English influence by their own and made an attempt to import fresh military forces from their settlements in Java. But the vigilance of Clive thwarted their design. They were defeated and humbled at Bedara in November, 1759, and sued for peace.
Clive thus maintained the supremacy of the English in Bengal for nearly three years, mainly by his personality and character. His departure on 25th February, 1760, was followed shortly by the death of Miran, the son of the Nawab, and the question of succession immediately came to the forefront. The treachery and incompetence of the Nawab and his failure to make the payments due to the Company made him and his family distasteful to the English. Holwell, the acting Governor, suggested the bold step of taking over the administration of the country, but the other members of the Council did not approve of the plan. He then supported the cause of Mir Kasim, the son-in-law of the Nawab, and Vansittart, the permanent Governor, acquiesced in this view.
A secret treaty was accordingly concluded with Mir Kasim on 27th September, 1760. Mir Kasim agreed to pay off the outstanding dues to the Company and also to cede the three districts of Burdwan, Midnapur and Chittagong. In return for these concessions the English offered to appoint him Deputy Subahdar and guaranteed his succession to the throne.
Neither the English nor the new Nawab took advantage of the new agreement to clear up the relations between the two parties. It was gradually becoming clear that, while the Nawab claimed to be an independent ruler, the English Authorities in Bengal had been acting in a manner which was incompatible with that position. It was evident that sooner or later the matter must come to a head, and the crisis came much earlier than was expected.
Vansittart followed throughout the policy of strengthening the hands of the Nawab. While Clive protected Ram Narayan, the deputy governor of Bihar, Vansittart handed him over to Mir Kasim who first robbed him and then put him to death. Having thus asserted his internal Autonomy, Mir Kasim felt strong enough to enter into that dispute with the English regarding inland trade which was to prove his ruin.
By an imperial firman the English Company enjoyed the right of trading in Bengal without the payment of transit dues or tolls. But the servants of the Company also claimed the same privileges for their private trade. The Nawabs had always protested against this abuse, but the members of the Council being materially interested, the practice went on increasing till it formed a subject of serious dispute between Mir Kasim and the English.
At last towards the end of 1762 Vansittart met Mr Kasim at Monghyr, where the Nawab had removed his capital, and concluded a definite agreement on the subject. The Council at Calcutta, however, rejected the agreement. Thereupon the Nawab decided to abolish the duties altogether; but the English clamoured against this and insisted upon having preferential treatment as against other traders.
Ellis, the chief of the English factory at Patna, violently asserted what he considered to be the rights and privileges of the English, and even made an attempt to seize the city of Patna. The attempt failed and his garrison was destroyed, but the events led to the outbreak of war between the English and Mir Kasim (1763).
On 10th June Major Adams took the field against Mir Kasim with about 1,100 Europeans and 4,000 sepoys. The Nawab assembled an army 15,000 strong, which included soldiers trained and disciplined on the European model. In spite of this disparity of numbers, the English gained successive victories at Katwah, Murshidabad, Giria, Sooty, Udaynala, and Monghyr. Mir Kasim fled to Patna, and after having killed all the English prisoners and a number of his prominent officials, went to Oudh. There he formed a confederacy with Nawab Shuja-ud-daulah and the Emperor Shah Alam II with a view to recovering Bengal from the English.
The confederate army was, however, defeated by the English general Major Hector Munro at Buxar on 22nd October, 1764. Shah ‘Alam immediately joined the English camp, and some time later concluded peace with the English. Mir Kasim fled, and led a wandering life till be died in obscurity, near Delhi, in -A.D. 1777.