The Spanish-American War The war between the United States and Spain was caused by unsettling tension between the two countries; Spain, at that time, one of the world's great powers, maintained colonies including Cuba, which lay only ninety miles from U.S. soil. Lasting from April until August, 1898, the war was fought to liberate Cuba from Spanish rule. During the course of the war the United States acquired Guam, Puerto Rico and the Philippines, and emerged as a world power. In 1823, James Monroe issued a bold proposal called the Monroe Doctrine, that stated one of the goals of the U.S. government was