Excerpts from Books and Wikipedia
". . . they used the captured Song fleet with its experienced captains and crews to send expeditions overseas. Yuan fleets of thousands of ships attempted to conquer Japan in 1174 and 1281, invaded Vietnam and Champa . . . and in 1292 Java, all without success. Burma and Siam were also invaded. While the Mongol warriors had an urge to expand, they did little to get China's sea trade into the early maritime world system that was beginning to take shape on the sea routes around Asia. Mongol rule brought China several decades of domestic peace and caravan trade across Asia. . . . The sea trade from West Asia and India was still largely in Arab hands because . . . the Islamic diaspora had brought Muslim merchants to China not only over the Silk Road but also by the Spice route that carried spices from the East Indies to China as well as to the eastern Mediterranean for Europe. Muslim merchant groups active in caravan trade across Central Asia as well as in maritime commerce were regulated and given loans by the Mongol rulers to invest in trade. . . . Commercial growth was signaled by the extensive issue of paper money, superintended by Muslim financiers at court." [Fairbank, p. 121-6]