Both East and West slid into new dark ages in which second-wave Axial thought (Christianity, Islam, and new forms of Buddhism) displaced older first-wave ideas, but in other ways their collapses were quite different. In the West, Germanic invaders broke up the less-developed part of the Roman Empire around the western Mediterranean, and the core retreated into its older and more developed heartland around the eastern Mediterranean. In the East, Inner Asian invaders broke up the older and more developed part of the former Han Empire around the Yellow River, and the core retreated into the
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