During the last phase of the Russian period (1825 to 1865), the Alaska Natives began to suffer the effects of introduced infectious diseases, to which they had no acquired immunity. In addition, their societies were disrupted by increasing reliance on European trade goods from the permanent Russian trading posts. A third influence were the early Russian Orthodox missionaries, who sought to convert the peoples to their form of Christianity. The missionaries learned native languages, and conducted services in those languages from the early decades of the 19th century. The Treaty of Saint Petersburg of 1825 defined the boundaries between Russian America and British Empire claims and possessions in the Pacific Northwest.