Iran, Iraq and Syria

Seljuq Bey, who laid the foundations for the Great Seljuq state, was the son of Duqaq Subashi, a commander of the state of Oghuz [Oğuz] near the Caspian Sea. On the death of his father, Seljuq Bey became subashi at a very young age and increased his power very quickly. To resolve conflicts with the sultan of the state of Oghuz, he surrounded himself with Oghuz Turks and settled at Jend near the Oxus River in AH 375 / AD 985 and converted to Islam.
Seljuq Bey allied himself to the Samanids and established himself at Nur near Bukhara, to defend the northern frontiers. He was succeeded by his son Arslan Bey. After the fall of the Samanids at the hands of the Karakhanids in 399 / 999, the good relationship the Seljuqs had enjoyed with the Karakhanids and the Ghaznavids came to an end.
The capture and imprisonment of Arslan Bey by the Ghaznavids in 416 / 1025 caused a split in the Seljuqs. Arslan Bey was succeeded by his nephews Tuğrul [Tughril] and Çağrı [Chaghrı]. Having defeated the Ghaznawids at Serahs (429 / 1038) and Dandanakan (431 / 1040), they founded the Great Seljuq state. Tuğrul Bey proclaimed himself sultan. Nishapur was briefly capital of the state, before being replaced by Marw.
The Great Seljuq state, founded in the territory of present-day Iran, saw its power increase significantly between 431 and 485 (1040–92), the years of the 'first imperial age'. Under the reigns of Alparslan [Alp Arslan] and Melikşah [Malik Shah], who succeeded Tuğrul Bey, the Seljuqs extended their dominion towards Anatolia, the Middle East and Central Asia.
After the death of Sultan Melikşah in 485 / 1092, disputes over succession, the Batini rebellions, the Turcoman revolts and the Mongol invasions caused the fragmentation of the Great Seljuqs into four states (the Seljuqs of Iraq, Syria, Kirman and Anatolia [Rum]) and the emergence of numerous atabegs [commanders]. In spite of the efforts of Sultan Sanjar, who came to power in 510 / 1117, to confederate the states, the Battle of Qatawan [Katvan] fought against the Karakhitais in 536 / 1141 and the Oghuz rebellions of 548 / 1153 paved the road to an inevitable end. The Great Seljuq state officially ceased to exist with the death of Sultan Sanjar in 552 / 1157.