Koch Hajo (1581-1616) was the kingdom under Raghudev and his son Parikshit Narayan of the Koch dynasty that stretched from Sankosh river in the west to the Bhareli river in the east on the north bank of the Brahmaputra river. It was created by dividing the Kamata kingdom then under Nara Narayan in medieval Assam. The Sankosh river divided the two new kingdoms, and it is roughly the boundary between the present-day Assam and West Bengal. The western half of the Kamata kingdom emerged as Koch Bihar whereas the eastern half emerged as Koch Hajo. The name Hajo comes from the legendary king Hajo, a Koch tribal chief and an ancestor of the Koch dynasty, who ruled over the Rangpur division in present-day Bangladesh and some regions of present-day Assam.
Division of Kamata kingdom
After the Koch–Ahom conflicts that saw Chilarai briefly occupy Garhgaon, the capital of the Ahom kingdom, Koch rule was consolidated between the Sankosh river in the west and the Subansiri river on the east under the governorship of Chilarai. Chilarai's son, Raghudev, was the heir apparent to the childless Nara Narayan. A son (Lakshmi Narayan) born late to Nara Narayan dashed Raghudev's hopes of becoming the king. Raghudev, accompanied by some trusted state officers, traveled east on a purported hunting trip and declared himself king of the eastern portion at a place called Barnagar near the Manas river. Nara Narayana did not react aggressively, and the kingdom was divided amicably with Raghudev promising to pay an annual tribute. This division occurred in 1581. When Nara Narayan died in 1587, Raghudev stopped paying tribute and declared himself independent.
Koch Hajo territory
The kingdom under Raghudev included the region between Sankosh and Bhareli rivers on the northern bank of the Brahmaputra river, and on the south the region west of the Kallang river that followed the course of the Brahmaputra as it bends south and right up to the forests of Mymensingh region, now in Bangladesh.
Raghudev Narayan
Raghudev's declaration of independence established a Koch Bihar-Koch Hajo conflict that was to result in Koch Bihar losing its independence to the Mughal Empire and Koch Hajo losing its very existence both within three decades. Lakshmi Narayan tried to instigate Parikshit, a son of Raghudev, against his father. The plot was detected and Parikshit managed to escape to Koch Bihar. This led to an armed conflict between the two kingdoms, but which maintained the status quo.
The first major defeat for Raghudev was at the hands of Isa Khan, an Afghan chief from Mymensingh. Raghudev fortified Jangalbari in Mymensingh, but ultimately lost the region south of Rangamati sometime before 1594. After Man Singh became the Subahdar of the Mughal Empire for Bengal in 1594 he led a campaign against Isa Khan and took possession of his territories; and when Isa Khan and others rallied the next year in 1596 they were effectively by Himmat Singh the son of Man Singh, forcing Isa Khan to ally with Raghudev. Raghudev, with the help of Isa Khan, attacked Bahirbandh in Koch Bihar, and Lakshmi Narayan submitted on his own accord to vassalage of the Mughal Empire. Under these circumstances, Raghudev transferred his capital from Barnagar to North Guwahati.
The Koch Bihar-Mughal alliance defeated Raghudev in May 1597, but in the same year Raghudev was able to recoup his losses with the help of Isa Khan. Isa Khan, who was able to rout the Mughal army and kill its commander Durjan Singh, a son of Man Singh, released the war prisoners and himself submitted himself to Akbar.
Having lost the alliance of Isa Khan, Raghudev was then forced to forge an alliance with the Ahom kingdom. Raghudev offered his daughter Mangaldoi to Prataap Singha in 1603, and the Ahom king accepted on the possibility of using Raghudev as a buffer against the Mughals. But this did not happen because Raghudev died within the same year after the marriage between Pratap Singha and Mangaldoi.
Parikshit Narayan
Parikshit the eldest son of Raghudev returned to the capital in 1603 to stake his claim to the kingdom. In the war of succession that followed, Man Singha, a son of Raghudev was offered refuge in Namrup by the Ahom king. Though Parikshit had earlier taken shelter with Lakshminarayan against his father Raghudev, he invaded Bahirbandh, a region under Koch Bihar and occupied it sometime between 1603 and 1608; and in the ensuing negotiations, won back the royal insignia that Raghudev had earlier lost to Lakhsminarayan. Lakshmi Narayan saw no recourse but to submit in person to Islam Khan in 1609. Parikshit could ward off the first Mughal expedition under Abdul Wahid.