Short answers, pulled from the story.
The primary cause of the Bengal War was the British East India Company's refusal to pay internal trade duties imposed by Nawab Mir Qasim. This economic dispute escalated into open conflict after the company demanded reinstatement of tax exemptions that had been abolished.
The main leaders opposing the British East India Company were Nawab Siraj ud-Daulah, his successor Mir Jafar, and later Mir Qasim. They formed an alliance with Mughal Emperor Shah Alam II and Awadhi Nawab Shuja-ud-Daula to halt British expansion in South Asia.
The Battle of Plassey occurred on the 23rd of June 1757 and resulted in the arrest and execution of Nawab Siraj ud-Daulah. This victory allowed the British East India Company to place Mir Jafar on the throne as a puppet ruler and establish dominance over Bengal.
The Treaty of Allahabad signed on the 16th of August 1765 officially ended the Anglo-Bengal War. This agreement granted the East India Company control over the Bengal diwani and established their sovereignty in Northern India through a fixed payment system.
The war transformed the British East India Company into an indispensable military and fiscal instrument for the Mughal Emperor Shah Alam II. By controlling the Bengal diwani, the company effectively became sovereign in Bengal and Northern India while the Mughal Empire lost direct administrative power.