Bengal — located in eastern India. It is consisted of the Ganga-Brahmaputra delta delta system and is bounded on the north by the Himalayas. We can identify several factors to justify treating Bengal as a historical region - it has had shared linguistic origins (Bengali) as well as shared political structures throughout the history of India. As for political organization, there have been a large number of states governing Bengal since antiquity.
The Bengal region
The Maratha empire, which spanned a significant portion of the Indian subcontinent c 1674 - 1818, but originated in the western Deccan Plateau (what is Maharashtra today). Other than shared political origin, we can identify a common linguistic (Marathi) and ethnic background (the Maratha and Kunbi castes) - at least in the Deccan Plateau where the empire originated.
The extent of the Maratha empire: https://en.wikipedia.org/wiki/File:India1760_1905.jpg
The Andaman Islands - We have good reason to state these islands as a historical region as their indigenous people have very strong ethnic and linguistic commonalities. In fact, they have not had any external influence for hundreds of years from ~200 BC till about the 1800s which makes them even more interesting as they have developed almost in complete isolation.
The Andaman Islands: https://en.wikipedia.org/wiki/File:Andaman_Islands.PNG
Southern India - We can analyze this entire geographical area as a historical region due to their common linguistic origins - the Indo-Dravidian language group. The inhabitants of this region are also derived from a common ethnic ancestry that is distinct from the Aryan origin of the majority of India. The time period of the origin of Dravidian is not clear but scholars have hypothesized that it might be around 2000-3000 BCE.
Distribution of the Dravidian languages: https://en.wikipedia.org/wiki/Dravidian_languages
Mizoram - We can consider it to be a historical region as the original inhabitants all share a common ancestry (Tibeto-Burman) and a shared linguistic history, situated within a common geographic area. The time period of the region is unclear but thought to be somewhere around the 5th century AD.
