In the 7th century, the new Muslim rulers institute the kharaj land tax, which led to mass migration of Babylonian Jews from the countryside to cities like Baghdad. This in turn led to greater wealth and international influence, as well as a more cosmopolitan outlook from Jewish thinkers such as Saadiah Gaon, who now deeply engaged with Western philosophy for the first time. When the Abbasid Caliphate and the city of Baghdad declined in the 10th century, many Babylonian Jews migrated to the Mediterranean region, contributing to the spread of Babylonian Jewish customs throughout the Jewish world.