World War I (1914–18)<span> CausesCauses of U.S. EntryMilitary and Diplomatic CourseDomestic CoursePostwar ImpactChanging Interpretations</span> <span>World War I (1914–18): Causes Although the </span>United States<span> did not enter World War I until 1917, the outbreak of that war in 1914, and its underlying causes and consequences, deeply and immediately affected America's position both at home and abroad.</span>