Excerpts from Books and Wikipedia
"As Seljuq power in Iran weakened, other dynasties began to step up in its place, including a resurgent Abbasid caliphate and the Khwarezmshahs. The Khwarezmid Empire was a Sunni Muslim Persianate dynasty, of East Turkic origin, that ruled in Central Asia. Originally vassals of the Seljuqs, they took advantage of the decline of the Seljuqs to expand into Iran. In 1194 the Khwarezmshah Ala ad-Din Tekish defeated the Seljuq sultan Toghrul III in battle and the Seljuq empire in Iran collapsed. Of the former Seljuq Empire, only the Sultanate of Rüm in Anatolia remained." [Wikipedia]