The Alaska Purchase

     Signed by president Andrew Johnson in 1867, the Alaska Purchase facilitated the sale of Russian America to the United States. Hoping to weaken British power in Canada after the Crimean War, and fearing a future conflict with Great Britain in which their colonies would be seized, the Russian government approached the U.S. in 1959 with an offer to sell the territory. The U.S. refused, being preoccupied with the risk of the Civil War, but the desire to sell the territory lingered in the Russian government. Again in 1867, after Union victory in the Civil War, the Tsar directed the Foreign minister to enter negotiations with the U.S. Secretary of State, William Seward. After an all-night session, a treaty was signed on March 30, 1867. The U.S. purchased the territory for 7.2 million dollars: about 2 cents per acre. Public opinion over the purchase was mixed, with some labeling it  "Seward's Folly" or "Seward's Icebox", arguing that there was no reason for the U.S. to annex a non-contiguous territory, or that the U.S. would absorb it anyway under the principles of Manifest Destiny, but most people understood that the economic gain derived from the purchase would make up for the cost, especially if gold was found.

Sources: https://www.ourdocuments.gov/doc.php?flash=true&doc=41#