French interest in northern Vietnam dated from the late 18th century, when the political Catholic priest Pigneau de Behaine recruited French volunteers to fight for Nguyễn Ánh and help begin the Nguyễn Dynasty in an attempt to gain privileges for France and the Roman Catholic Church. In 1858, France began their colonial campaign and in 1862 annexed several southern provinces of Vietnam to become the colony of Cochinchina, laying the foundations for its later colonial empire in Indochina. French explorers followed the course of the Red River (Asia) through northern Vietnam to its source in Yunnan, arousing hopes that an extremely profitable overland trade route could be established with China, bypassing the treaty ports of the Chinese coastal provinces. The main obstacle to the realisation