Bengal vs Bangladesh
How do you differentiate between a land of composite culture by drawing a line across it and dividing it into two different countries on the basis of religion? This is exactly what happened when the British divided the Indian province of Bengal into two Bengals, West Bengal and East Bengal. The fact is that, this division was totally unrealistic and not done for any betterment or development of the area but only to suit political purposes. There are lots of similarities between Bengal and Bangladesh, though there are differences also that will be highlighted in this article.
When British left India, they crafted East Bengal out of Bengal and gave it to Pakistan, and this meant that India had Pakistan on both of its flanks, west, as well as east. Indian part of Bengal was termed West Bengal, while the one handed over to Pakistan was called East Bengal just because it was further east in the direction. The basis of bifurcation of Bengal was administrative at first, when it was attempted in 1905 and 1911. Then Dhaka was made administrative capital of East Bengal. However, when Pakistan was created, religion formed the basis for it being given to Pakistan as majority of the population was Muslim in East Bengal. Even after independence, East Bengal was dominated by the rich and powerful classes from the western part of Pakistan, and this led to a massive revolt led by people of East Bengal against oppression by Punjabis. This movement was supported by Indian Army, and finally East Bengal got independence from Pakistan, and Bangladesh came into existence.
Talking about differences between the two Bengals, a person born in West Bengal is just Bengali, while a person born in Bangladesh is referred to as Bangladeshi Bengali. While 80% of the populace in West Bengal is Hindu, 80% of the population is Muslim in Bangladesh. Despite religious differences, there are cultural similarities, which mean that a person is Calcutta feels culturally similar to a Bangladeshi than a Marathi or a Gujarati person. This is mainly because of Bengali language, which is the official language in both Bengals (read West Bengal and Bangladesh).
While Bangladesh is a full fledged independent country, West Bengal is only a state (important one though) in the Union of India. Calcutta (now called Kolkata) was the center of whole of undivided Bengal until British divided it into west and East Bengal with Dhaka being made the capital of East Bengal. A person born in Bengal is an Indian first and then Bengali while a person born in Bangladesh is always a Bangladeshi. While Bangladesh is a parliamentary democracy, Bengal too follows the same democracy though it has been traditionally ruled by Left parties.
Bangladesh is unique in the sense that it has only one ethnic group living in there which is why there is no sectarian or ethnic violence seen in the country.
Summary
If one hears the term Bengali, he is actually listening about either a language or a cultural group that is not limited to West Bengal or Bangladesh as people of this ethnicity are spread in many parts of the world, especially South East Asia. A Bengali person is not automatically a Bangladeshi, as he could belong to Pakistan, India, or Bangladesh. All Bangladeshis are Bengalis, but not all Bengalis are Bangladeshis.