Ethnically, the Chakmas are Mongoloid Chagtai, and are thus closely related to Chagtai Mughal, Barua and Mogh tribes. Their ancestors were solders of Mughal Empire Humayun. When Hamayun temporarily lost his throne by Sher Khan, And one of largest group of Mughal solders moved from Suba-i-Bangala of India to settle in the Arakan.They did inter marriage with Mogh tribe and Barua tribe. Most of the Chakma people later moved to eastern Bengal (present day Bangladesh), settling in the Cox's Bazar District, the Korpos Mohal area, and areas of present Mizoram. The Chakmas were historically the rulers of Chittagong Hill Tracts under the control of a king. Today, however, the power of the Chakma king, Raja Debashish Roy, is merely symbolic.
The Arakanese referred to the Chakmas as Saks or Theks,It's means mix people. In 1546, when the king of Arakan, Meng Beng, was engaged in a battle with the Burmese, the Sak chief appeared from the north and attacked Arakan, and occupied the Ramu of Cox's Bazar.
Diego de Astor, a Portuguese, drew a map of Bengal, which was published as Descripção do Reino de Bengalla in the book Quarta decada da Asia(Fourth decade of Asia) by João de Barros in 1615. The map shows a place called "Chacomas" on the eastern bank of the river Karnaphuli, suggesting that this is where the Chakmas used to live at the time of the drawing of the map. The Arakan king Meng Rajagri who is also known as Salim Shah (1593-1612) conquered this land, and in 1607 in a letter to a Portuguese merchant, Philip de Brito Nicote, addressed himself as the highest and most powerful king of Arakan, of Chacomas and of Bengal.
Defeated by the Arakanese, the Chakmas entered present day Chittagong Hill Tracts and made Alekyangdong, present-day Alikadam, their capital. From Alekyangdong they went north and settled in present day Rangunia, Rauzan, and Fatikchari upazillas of Chittagong District.
In 1666, Shaista Khan, who was then Mughal Governor of Bengal, defeated the Arakanese, conquered Chittagong, and renamed it Islamabad.However, in the early days Mughal supremacy in the region was confined only to the plain areas of Chittagong, and the Chakmas remained practically unaffected by Mughal advances. After a few years, when a dispute developed between the Mughals and the Chakmas, the Mughals demanded tribute from the Chakmas for trading with Chittagong.
In 1713, peace was established, and soon a stable relationship developed between the Chakmas and the Mughals; the latter never demanded complete subjugation from the former. The Mughals also rewarded the Chakma King Sukdev or Khush Khan, who established a new capital in his own name, in an area which is still known as Sukbilash. There are still ruins of the royal palace & other establishments. Subsequently the capital was shifted to Rajanagar.
Three years after the Battle of Plassey, Mir Qasim the new Nawab of Murshidabad rewarded the British East India Company with Chittagong, Burdwan and Midnapur. On 5 January 1761 the Company representative Harry Verlest took over charges of Chittagong from Subedar Mohammad Reza Khan. But the Chakma King Sher Doulat Khan who was practically independent though nominally paid tribute to the Mughals, did not accept the hegemony of the Company and their demand of taxes at a enhanced rate. A protracted war started and it continued up to 1787. The East India Company launched four offensives against the Chakmas in 1770, 1780, 1782 and 1785. In 1785 the Company started peace negotiations with the then Chakma King Jan Baksh Khan, son of Sher Doulat Khan. Later in 1787 the King accepted the sovereignty of the Company and agreed to pay 500 maunds of cotton annually. A peace agreement or treaty was signed at Kolkata.