1905 partition of Bengal
The decision to effect the Partition of Bengal (Bengali: বঙ্গভঙ্গ) was announced in July 1905 by the Viceroy of India, Lord Curzon. The partition took place on 16 October 1905 and separated the largely Muslim eastern areas from the largely Hindu western areas. The Hindus of West Bengal who dominated Bengal's business and rural life complained that the division would make them a minority in a province that would incorporate the province of Bihar and Orissa. Hindus were outraged at what they recognised as a "divide and rule" policy, where the colonisers turned the native population against itself in order to rule, even though Curzon stressed it would produce administrative efficiency. The partition animated the Hindus and led the Muslims to form their own national organisation on communal lines. Bengal was reunited in 1911 in an effort to appease Bengali sentiment and make administration easier.
The provincial state of Bengal had an area of 189,000 mi2 and a population of nearly 78.5 million. It included the Hindi-speaking regions of Bihar, the Odia-speaking regions of Odisha as well as the Assamese-speaking region of Assam, making it a huge administrative entity. Moreover, the capital, Calcutta, was also the capital of the entire British India. With the growing efforts of the Indian National Congress to secure the independence of India, Lord Curzon decided to address both these problems by partitioning Bengal into two entities, which would result in a Muslim-majority in the eastern half, and a Hindu-majority in the western half. This he hoped would reduce the administrative pressures and divide the population on religious grounds, quelling the Indian Independence Movement.
...
Wikipedia