How was the American Acquisition of Alaska and Hawaii controversial

Russia offered to sell Alaska to the United States in 1859, believing the United States would off-set the designs of Russia's greatest rival in the Pacific, Great Britain. The Senate approved the treaty of purchase on April 9; President Andrew Johnson signed the treaty on May 28, and Alaska was formally transferred to the United States on October 18, 1867. This purchase ended Russia's presence in North America and ensured U. S. access to the Pacific northern rim.