Upon Happer's arrival in Macau on October 23, 1844, the Opium War had previously blocked most forms of western and missionary influence in China. Ability to travel throughout China had been very restricted for foreigners. Although access to Canton was still officially restricted, Happer reached the people through the provision of medical aid and preaching the gospel. Following the Opium War, the Treaty of Nanking opened five ports for foreign trade. As a result, China became open to missionaries. As one of only 31 Protestant missionaries (3 of them Presbyterian, Happer faced numerous challenges and difficulties. Few resources were available, with China as an intimidating location. Foreigners were not allowed to live in Canton so Happer moved to Hong Kong and worked and later led at the Morrison Education Society.