Hold on. Abbasid or Abbasid. Ah, I'm right twice! Right, so the Abbasids were from the Abbasi, or Abbasi family, which hailed from one of the eastern and therefore more Persian provinces of the Islamic Empire. The Abbasids took over in 750 and no one could fully defeat them until 1258 when they were conquered by, wait for it, the Mongols. The Abbasids kept the idea of a hereditary monarchy, but they moved the capital of the empire to Baghdad and they were much more welcoming of non-Arab Muslims into positions of power. And under the Abbasids, the Dar al-Islam took on a distinctly Persian cast that it never really lost.