The Spanish-American War only lasted 100 days, cost the United States almost nothing in terms of casualties and brought the country significant gains in territory, turning the former set of colonies into an empire of her own and prompting Secretary of State John Hay to write to Theodore Roosevelt that the conflict was "a splendid little war, begun with the highest motives... favored by that Fortune which loves the brave."
In contrast with World War I, which occurred 20 years later, the Spanish-American War represented the end of an era of warfare. World War I claimed more than 37 million dead and wounded and resolved very little in terms of the hostilities that flamed throughout Europe. The Spanish-American War, on the other hand, claimed about 100,000 fatalities, with half of those resulting from diseases that the Spanish military contracted in Cuba and the Philippines. The shock with which President Woodrow Wilson learned about the horrors of World War I led him to urge the creation of a League of Nations to broker peace between hostile countries, while the after effects of the Spanish-American War induced President Theodore Roosevelt's determination to "talk softly and carry a big stick." The gravity of warfare was not part of American considerations after defeating Spain.