Chaghri and Tughril have fought against the Ghaznavids between 1038 and 1040, usually with hit and run maneuvers.
When the Seljuq leaders begin raising an army, they are seen as a threat to the Ghaznavid territories.
Following the looting of border cities by Seljuq raids, Sultan Mas'ud I decides to expel the Seljuqs from his territories.
Tughril had suggested to continue with the hit and run operations, but Chagri, who commands the Seljuq army, prefers to fight.
During the march of Sultan Mas'ud's army to Sarakhs, the Seljuq raiders harass the Ghaznavid army with hit-and-run tactics.
Seljuq raiders also destroye the supply lines of the Ghaznavids, cutting them off from the nearby water wells.
The discipline and morale of the Ghaznavid army drops precipitously.
Finally, on May 23, 1040, around twenty thousand Seljuq soldiers engage in battle with an estimated fifty thousand Ghaznavid soldiers in Dandanaqan, between Merv and Sarakhs; the Seljuqs are victorious.
They soon occupy Khorasan and the cities of the area, encountering little resistance.
A kurultai is held after the battle, by which the nascent empire is divided between the two brothers.
While Tughril reigns in the west (comprising modern western Iran, Azerbaijan and Iraq), Chaghri reigns in eastern Iran, Turkmenistan, and Afghanistan.
