This geographical contrast made a world of difference. By 450 CE a new frontier of rice agriculture had begun booming around the Yangzi; by 600 China had been reunited; and over the following century the Grand Canal, linking the Yangzi and Yellow rivers, gave China a system of internal waterways that functioned rather like the Mediterranean had done for ancient Rome. In the West, though, where the Arab invaders were strong enough to break up the old Mediterranean core but not strong enough to remake it, social development kept falling until 700.
