Final answer:
Roosevelt became a hero during the Spanish-American War through his leadership of the Rough Rider Regiment at the battle of San Juan. His role was pivotal in his rise to popularity and his subsequent political career, marking the United States' growing international presence.
Step-by-step explanation:
Roosevelt became a hero during the Spanish-American War. As lieutenant colonel of the Rough Rider Regiment, he led a charge at the battle of San Juan. This notably conspicuous role in the war elevated him to the status of war hero. Roosevelt saw the war as not only an adventure but as a chance for national revitalization through a martial ethic, as well as a duty from a standpoint of national honor to help Cuba.
In the context of American expansion, the war was a significant international conflict and marked the United States' entry onto the world stage. Although the African American Buffalo Soldiers also played a heroic role in the conflict, it was Roosevelt's charge up Kettle Hill that captured the public's imagination and contributed to his heroic image, something he personally chronicled in his memoir, The Rough Riders.
Roosevelt's participation in the Spanish-American War not only established him as a military hero but also propelled his political career forward. After the war, he returned to New York and was elected governor, and subsequently, his military fame would contribute to his selection as Vice President under President McKinley.