一口通商
From 1757 to signature of the Treaty of Nanking by the Chinese and British governments in 1842, all foreign trade in China operated through the monopoly Canton System centered on the Southern Chinese port of Canton (now Guangzhou). The treaty abolished this monopoly and opened the further ports of Shanghai, Amoy (Xiamen), Ningpo (Ningbo) and Foochow (Fuzhou) to international trade and brought with it the need for a mechanism to collect customs duties payable on business transacted in these places.