Bengal is a geopolitical, cultural and historical region in Asia, which is located in South Asia at the apex of the Bay of Bengal.
Geographically, it is made up by the Ganges-Brahmaputra delta system, the largest such formation in the world; along with mountains in its north bordering the Himalayan states of Nepal and Bhutan and east bordering Burma.Politically, Bengal is now divided between the sovereign Republic of Bangladesh and India. Bangladesh a sovereign state the name means 'Bengali Country' or 'Country of Bengal'
In spite of a last-ditch effort to form a United Bengal, when India gained independence in 1947, Bengal was partitioned along religious lines. 
Bengal was conquered by the British East India Company in the Battle of Palasy 1757 and and became the Bengal Presidency, which experienced deindustrialization and famines under British rule.
Bengal played a major role in the Indian independence movement, in which revolutionary groups were dominant. Armed attempts to overthrow the British Raj began with the rebellion of Titumir, and reached a climax when Subhas Chandra Bose led the Indian National Army against the British. Bengal was also central in the rising political awareness of the Muslim population—the All-India Muslim League was established in Dhaka in 1906.
The United Kingdom Cabinet Mission of 1946 to British Raj aimed to discuss the transfer of power from the British government to the Indian leadership. Bengali Prime Minister Huseyn Shaheed Suhrawardy and nationalist leader Sarat Chandra Bose wanted to found a united and independent nation-state of Bengal. The proposal was floated as an alternative to the partition of Bengal on communal lines. The initiative failed due to British diplomacy and communal conflict between Muslims and Hindus that eventually led to the second partition of Bengal.

Bengal Presidency 1858The Partition of Bengal Presidency in 1947 resulted in Bengal's division on religious grounds, between the India and Pakistan prominently called Radcliffe's line. 

Pakistan( Todays Independent Bangladesh): East Dinajpur, Rangpur, Dhaka, Rajshahi, Bogra, Pabna, Mymensingh, Sylhet (except Barak valley), Khulna, Bakerganj, Tippera, Noakhali, Chittagong, Jessore, East Nadia, Chittagong Track Hills.
India: West Dinajpur, Jalpaiguri, Darjeeling, Malda, Murshidabad, West Nadia, Calcutta, 24 Pargana, Burdwan, Birbhum, Midnapore,  Howrah, Hooghly, Assam,and the Princely state of Tripura,  Naga hills, Manipur,coch Bihar, Khasi state under the protection of India.
Radcliffe's line split Bengal, which historically was always a single economic zone, single cultural and ethnic (Bengali-Hindu or Bengali-Muslim) zone, into two halves. The two-halves were intricately connected with each other. The fertile East produced food and raw materials which the West consumed and the industrialized West produced manufactured goods which were consumed by the East. This mutually beneficial trade and exchange was severely disrupted by the partition. Rail, road and water communication routes were severed between the two.

The predominant ethno-linguistic group is the Bengali people, who speak the Indo-Aryan Bengali language.
Own work based on: Blankmap-ao-270W-asia.png  and Bengal Presidency 1858.png
Aziz Tarak.