Final answer:
Theodore Roosevelt became president after the Spanish-American War when he succeeded the assassinated President William McKinley in 1901.
Step-by-step explanation:
Theodore Roosevelt became president after the Spanish-American War. During the war, he was a lieutenant colonel of the Rough Rider Regiment and became a national hero for leading a charge at the Battle of San Juan Hill. Roosevelt was then elected governor of New York and, later, became Vice President under President William McKinley. McKinley's assassination in 1901 propelled Roosevelt to the presidency, making him the youngest President in the nation's history at that time. His presidency initiated a new era of progressive policies and transformative leadership.