United States imperialism affected Alaska by the US not owning Alaska and in 1868 the US bought Alaska from Russia for 7.2 million dollars. This is known as the treaty of Russia. Most of Alaska was unexplored at the time William H. Seward agreed to purchase it on March 30, 1867. The Seward folly made an increase in imperialism. The decision to buy Alaska helped the United States out by stopping Spanish and Russian expansion into the United states and it made the United States about 20% bigger. And buying Alaska put an end to russian trade expansion in the pacific northwest and the Us can control the area without European competition The americans had thought Seward just bought useless land because it had so much ice on it. Little did they