And under the Abbasids, the Dar al-Islam took on a distinctly Persian cast that it never really lost. The caliph now styled himself as a king of kings, just like the Achaemenids had, and pretty soon the caliph's rule was a lot more indirect, just like the original Persians. This meant that his control was much weaker, and by about 1000 CE, the Islamic Caliphate, which looks so incredibly impressive on a map, had really descended into a series of smaller kingdoms, each paying lip service to the caliph in Baghdad. This was partly because the Islamic Empire relied more and more on soldiers from the frontier, in this case the Turks, and also slaves pressed into military service in order to be the backbone of their army, a strategy that has been tried over and over again and has worked exactly zero times, which you should remember if you ever become an emperor. Actually, our resident historian points out that that strategy has worked, if you are the Mongols. More important than the Persian-style monarchy that the Abbasids set up was their openness to foreigners and their ideas. That tolerance and curiosity ushered in a golden age of Islamic learning centered in Baghdad.