sentences:  The major portion of Alaska remained little known, and the Yup'ik Eskimo of the Yukon-Kuskokwim delta were not strongly affected.The Russo-American Treaty of 1824 was signed in St. Petersburg between representatives of Russian Empire and the United States on April 17, 1824, and went into effect on January 12, 1825.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.