After the collapse of the Classical Empires, the next great civilization that arises is that of the Arab Islamic Caliphates. Beginning with Muhammad recieving Allah's message in 610 CE, the Post-Classical Period begins with the Arabs expanding into the areas seen below. The Muslims will dominate trade, astronomy, mathematics, science, philosophy, etc. throughout the era. (I like to break the Post-Classical period into M&M: Muslims & Mongols. There are other great civilizations and ideas(trade, Tang/Song China, migrations, etc.); but all other Afro-Eurasian societies must deal with these two powerful entities. In AP terms, you should devote some time to the Islamic Caliphates. If you feel that you don't know that much about Islam and its impact; you're right. DOUBLE-DOWN HERE! KNOW ISLAM!