Xiamen Island was considered to possess one of the world's great natural harbors in Yundang Bay, but Fujian's international trade was long restricted to Quanzhou or to Guangzhou in Guangdong. Due to the siltification of Quanzhou's harbor, the British insisted that Xiamen be opened to foreign trade in the treaty that ended the First Opium War in 1842. Under the Qing, both before and after the war, there was large-scale emigration of Chinese from southern Fujian spread Hokkien-speaking communities to Singapore, Malaysia's Penang, Indonesia's Riau Province and the Philippines. The overseas Chinese continue to support Xiamen's educational and cultural institutions. As part of China's Opening Up Policy under Deng Xiaoping, Xiamen became one of the original four special economic zones opened to foreign investment and trade in the early 1980s. Its former harbor was enclosed using land excavated during the city's expansion.