Even when the emperors did their utmost to keep them at home, the Chinese ventured overseas in search of knowledge, fortune and adventure. Manchu Qing rulers thought those who left must be criminals or conspirators and once forced the entire coastal population of southern China to move at least 10 miles inland.

But even that didn't put an end to wanderlust. Sailing junks ferried merchants to Manila on monsoon winds to trade silk and porcelain for silver. And in the 19th century, steamships carried armies of "coolies"...