What were the main causes of conflict between East India Company and the Nawab of Bengal?

The conflicts between the British East India Company and the new Nawab of Bengal, Siraj ud-Daulah, erupted when the young ruler objected to the British strengthening their presence with a massive fort at Calcutta (Kolkata).
The conflict went far beyond differences in economic policy and trade practices. In 1756 the Nawab’s troops took over the city and the new fort; there were some 50,000 Indian soldiers, but the British had less than 200 men. With their victory, the Bengalis imprisoned the British in their own fort, putting about 150 people into what became known as the infamous Black Hole.
In 1757, the tides were finally turned with the Battle of Plassey. Robert Clive, a former military office, was the East India Company administrator who led the British campaign. He unilaterally appointed a new Nawab, Mir Jafar, and placed him at the head of the combined British and Indian forces, which defeated Siraj ud-Daulah's troops to retake Calcultta. This episode effectively ended strong opposition to the East India Company’s practices, and the company’s presence in many parts of India amounted to de facto rule, including a strong military component.
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