The Russian colonization of the Americas covers the period from 1732 to 1867, when the Russian Empire laid claim to northern Pacific Coast territories in the Americas. Russian colonial possessions in the Americas are collectively known as Russian America. Russian expansion eastward began in 1552, and in 1639 Russian explorers reached the Pacific Ocean. In 1725, Emperor Peter the Great ordered navigator Vitus Bering to explore the North Pacific for potential colonization. The Russians were primarily interested in the abundance of fur-bearing mammals on Alaska's coast, as stocks had been depleted by overhunting in Siberia. Bering's first voyage was foiled by thick fog and ice, but in 1741 a second voyage by Bering and Aleksei Chirikov made sight of the North American mainland.