Between 1020 and 1040 CE, the Oghuz Turks, also known as Turkmens, led by Seljuq's son Musa and nephews Tughril and Chaghri, migrated to Iran. Initially, they moved south to Transoxiana and then to Khorasan, drawn by local rulers' invitations and subsequent alliances and conflicts. Notably, other Oghuz Turks had already settled in Khorasan, particularly around the Kopet Dag mountains, an area extending from the Caspian Sea to Merv in modern-day Turkmenistan. This early presence is evidenced by references to locations such as Dahistan, Farawa, Nasa, and Sarakhs in contemporary sources, all situated in today's Turkmenistan.

Around 1034, Tughril and Chaghri were soundly defeated by the Oghuz Yabghu Ali Tegin and his allies, forcing them to escape from Transoxiana. Initially, Turkmens took refuge in Khwarazm, which served as one of their traditional pastures, but they were also encouraged by the local Ghaznavid governor, Harun, who hoped to utilise Seljuks for his efforts to seize Khorasan from his sovereign. When Harun was assassinated by Ghaznavid agents in 1035, they again had to flee, this time heading south across the Karakum Desert. First, Turkmens made their way to the important city of Merv, but perhaps due to its strong fortification, they then changed their route westwards to take refuge in Nasa. Finally, they arrived on the edges of Khorasan, the province considered a jewel in the Ghaznavid crown.

The Seljuks defeated the Ghaznavids at the Battle of Nasa Plains in 1035. Seljuk's grandsons, Tughril and Chaghri, received the insignias of governor, grants of land, and were given the title of dehqan.^[5]

Initially the Seljuks were repulsed by Mahmud and retired to Khwarezm, but Tughril and Chaghri led them to capture Merv and Nishapur (1037/38). Later they repeatedly raided and traded territory with his successor, Mas'ud, across Khorasan and Balkh. They begin to settle in eastern Persia.