Brahmaputra Valley in the context of "Kamarupa"

The Bengal Sultanate (Middle Bengali: শাহী বাঙ্গালাহ্, Classical Persian: سلطنت بنگاله) was a late medieval sultanate based in the Bengal region in eastern South Asia between the 14th and 16th century. It was the dominant power of the Ganges-Brahmaputra Delta, with a network of mint towns spread across the region. The Bengal Sultanate had a circle of vassal states in the Indian subcontinent and Southeast Asia, including parts of Odisha in the southwest, parts of Bihar in the northwest, parts of Assam in the northeast, Arakan in the southeast, and Tripura in the east.

The Bengal Sultanate controlled large parts of eastern South Asia during its five dynastic periods, reaching its peak under Jalaluddin Muhammad Shah. Its raids and conquests reached Nepal in the north, Brahmaputra Valley (modern-day Assam) in the east, and Jaunpur and Varanasi in the west. It was reputed as a thriving trading nation. Its decline began with an interregnum by the Sur Empire, followed by Mughal conquest and disintegration into petty kingdoms. The Bengal Sultanate was a Sunni Muslim monarchy with Bengali, Turco-Persian, Afghan and Abyssinian elites. The most prominent dynasties were the Ilyas Shahi, House of Ganesha and Hussain Shahi. The kingdom was known for its religious pluralism where non-Muslim communities co-existed peacefully. While Persian was used as the primary official, diplomatic and commercial language, it was under the Sultans that Bengali first received court recognition as an official language. The cities of the Bengal Sultanate are termed as Mint Towns where the historical taka was minted. These cities were adorned with stately medieval buildings. In 1500, the royal capital of Gaur was the fifth-most populous city in the world. Other notable cities included the initial royal capital of Pandua, the economic hub of Sonargaon, the Mosque City of Bagerhat, and the seaport and trading hub of Chittagong. The Bengal Sultanate was connected to states in Asia, Africa, the Indian Ocean, and Europe through maritime links and overland trade routes. The Bengal Sultanate was a major trading center on the coast of the Bay of Bengal. It attracted immigrants and traders from different parts of the world. Bengali ships and merchants traded across the region, including in Malacca, China, and the Maldives.

The Lower Himalayan Range, also called the Lesser Himalayas and Mahabharat Lekh or Himachal, is one of the four parallel sub-ranges of the Himalayas. It has the Great Himalayas to the north and the Sivalik Hills to the south. It extends from the Indus River Basin to the Brahmaputra Valley, traversing across Afghanistan, Pakistan, India, Nepal China and Bhutan. The sub-range has an average elevation of 3,700–4,500 m (12,100–14,800 ft).

Assam is a state in northeastern India, south of the eastern Himalayas along the Brahmaputra and Barak River valleys. Assam covers an area of 78,438 km (30,285 sq mi). It is the second largest state in northeastern India by area and the largest in terms of population, with more than 31 million inhabitants. The state is bordered by Bhutan and Arunachal Pradesh to the north; Nagaland and Manipur to the east; Meghalaya, Tripura, Mizoram and Bangladesh to the south; and West Bengal to the west via the Siliguri Corridor, a 22-kilometre-wide (14 mi) strip of land that connects the state to the rest of India. Assamese and Bodo are two of the official languages for the entire state and Meitei (Manipuri) is recognised as an additional official language in three districts of Barak Valley and Hojai district. in Hojai district and for the Barak Valley region, alongside Bengali, which is also an official language in the Barak Valley.

The state has 35 districts with 5 divisions. Guwahati (containing the state capital Dispur) is the largest city in northeastern India. Assam is known for Assam tea and Assam silk. The state was the first site for oil drilling in Asia. Assam is home to the one-horned Indian rhinoceros, along with the wild water buffalo, pygmy hog, tiger and various species of Asiatic birds, and provides one of the last wild habitats for the Asian elephant. The Assamese economy is aided by wildlife tourism to Kaziranga National Park and Manas National Park, which are World Heritage Sites. Dibru-Saikhowa National Park is famed for its feral horses. Sal tree forests are found in the state which, as a result of abundant rainfall, look green all year round. Assam receives more rainfall than most parts of India; this rain feeds the Brahmaputra River, whose tributaries and oxbow lakes provide the region with a distinctive hydro-geomorphic environment.

The Assamese people are a socio-ethnic linguistic identity that has been described at various times as nationalistic or micro-nationalistic. This group is often associated with the Assamese language, the easternmost Indo-Aryan language, and Assamese people mostly live in the Brahmaputra Valley region of Assam, where they are native and constitute around 56% of the valley's population. The use of the term precedes the name of the language or the people. It has also been used retrospectively to the people of Assam before the term "Assamese" came into use. They are an ethnically diverse group formed after centuries of assimilation of Austroasiatic, Tibeto-Burman, Indo-Aryan and Tai populations, and constitute a tribal-caste continuum—though not all Assamese people are Hindus and ethnic Assamese Muslims numbering around 42 lakh (4,200,000) constitute a significant part of this identity. The total population of Assamese speakers in Assam is nearly 15.09 million which makes up 48.38% of the population of state according to the Language census of 2011.

The U Go offensive, or Operation C (Japanese: ウ号作戦, U Gō sakusen), was the Japanese offensive launched in March 1944 against forces of the British Empire in the northeast Indian regions of Manipur and the Naga Hills (then administered as part of Assam). Aimed at the Brahmaputra Valley, through the towns of Imphal and Kohima, the offensive along with the overlapping Ha Go offensive was one of the last Japanese offensives during the Second World War. The offensive culminated in the Battles of Imphal and Kohima, where the Japanese and their allies were first held and then pushed back.

The Ahom (Pron: /ˈɑːhɒm/) or Tai-Ahom (Ahom: 𑜄𑜩 𑜒𑜑𑜪𑜨; Assamese: টাই-আহোম) is an ethnic group from the Indian states of Assam and Arunachal Pradesh. The members of this group are admixed descendants of the Tai peoples who reached the Brahmaputra Valley of Assam in 1228, along with indigenous peoples who joined them over the course of history. Sukaphaa, the leader of the Tai group and his 9,000 followers, established the Ahom kingdom (1228–1826), which controlled much of the Brahmaputra Valley (now in Assam) until 1826, when the Treaty of Yandabo was signed.

The modern Ahom people and their culture are a syncretism of Tai and local Tibeto-Burman speakers. The mixture of immigrants and local peoples who underwent Ahomisation came to be known as Ahom.