1) In the late 19th century, American leaders began pushing for the U.S. to join European nations in establishing overseas colonies, beginning the era of American imperialism. 2) The U.S. acquired Alaska from Russia in 1867 and annexed Hawaii in 1898, seeing their strategic value. 3) The sinking of the U.S.S. Maine in Cuba in 1898 helped spark the Spanish-American War, leading the U.S. to gain control of Puerto Rico, Guam, and the Philippines. The U.S. thus emerged as a new world power.