The dynasty controlled the areas we today know as Tirhut or Mithila in the state of Bihar, India and adjoining parts of South Eastern Nepal.

[7] According to French orientalist and indologist Sylvain Lévi, Nanyadeva established his supremacy over Simraungadh probably with the help of the Chalukya king Vikramaditya VI.

[8][9][10] After the reign of Vikramaditya VI in 1076 CE, he led a successful military campaign against the Pala Empire and the Sena dynasty.

[14] The Karnat kings referred to themselves with the title of Mithileśwara[15] and the first recorded piece of Maithili literature, the Varna Ratnakara was also composed during their rule.

Sena dynasty inscriptions refer to Nanyadeva as Karnata-Kulabhusana indicating that he had his origins in the South and likely arrived in the North through the Chalukya invasions.

His ancestors were petty chieftains and adventurers in Eastern India who arrived in the territory of the Pala Empire to work as officials and later carved out their own principalities while also asserting their independence.

In the wake of the Varendra rebellion, the Palas grip on the region was substantially weakened and this provided an opportunity for Nanyadeva to assert his independence.

[18] When Nanyadeva first arrived in the region in 1093 A.D., he originally established his stronghold in Nanapura in Champaran, Bihar and referred to himself as Mahashamantadhipati as confirmed by the local traditions of Mithila.

[19] The reign of Nanyadeva can be precisely dated by an inscribed stone pillar at Simraungadh which says, translated into English, "In the Śaka year 1019, on Saturday, the 7th of śrāvaṇa, in the śvāti nakṣatra, king Nānyadeva took the land.

[20]: 240–1 Another event that happened during Nanyadeva's reign was a clash of some sort with the Sena ruler Vijayasena, possibly because both of them were trying to win territory in the east.

Whatever the exact nature of this event, it seems to have left Nanyadeva a "negligible factor in North Indian politics" compared to the Senas and Gahadavalas.

According to Upendra Thakur, Nanyadeva may have championed Śivadeva, a prince of the Thakuri dynasty (which had been dethroned by another branch by around 1080), in his bid for the throne.

[20]: 252–3 According to local tradition, Nanyadeva's original capital was at Nānyapura in the present-day Champaran districts of Bihar, where ruins are still visible.

Whenever the shift happened, Simraungadh went on to serve as the main capital for the later Karnat rulers, while Nānyapura ended up becoming abandoned, and no later traditions or documents mention it.

The 15th-century poet, Vidyapati asserted in his writings that Malladeva was a "valiant warrior" and he spent time in the kingdoms of the neighbouring Gahadavala dynasty and the Pithipatis of Bodh Gaya.

[18] The Ramacharitam attests to the invasion of the Gauda region by Gangadeva during his rule in Mithila at some point after 1147 CE which during this period was held by Madanapala.

[23] Harisimhadeva turned out to be the last king of the Karnata dynasty as he didn't show his strength and left the fort when he heard the news of an army of the Tughlaq Sultan approaching Simraungarh.

[28] The culture of Mithila was also orthodox and conservative and this conservatism was reinforced by the institution of Kulinism which as per local tradition, was introduced by the final Karnat King, Harisimhadeva.

[29] An inscribed of Vishnu has been recovered from the village of Andhra Tharhi in Madhubani district and records that it was donated by a Karnat minister by the name of Śrīdharaṇadāsa during the rule of Nanyadeva.

[29] Under the Karnatas, Mithila experienced a period of relative peace which allowed authors, poets and artists to receive royal patronage.