He resigned to help form and lead the Rough Riders, a unit that fought the Spanish army in Cuba to great publicity. Returning a war hero, Roosevelt was elected governor of New York in 1898. The New York state party leadership disliked his ambitious agenda and convinced McKinley to choose him as his running mate in the 1900 election. Roosevelt campaigned vigorously and the McKinley–Roosevelt ticket won a landslide victory based on a platform of victory, peace, and prosperity.
Roosevelt assumed the presidency at age 42, and remains the youngest person to become president of the United States. As a leader of the progressive movement he championed his "Square Deal" domestic policies. It called for fairness for all citizens, breaking of bad trusts, regulation of railroads, and pure food and drugs. Roosevelt prioritized conservation and established national parks, forests, and monuments to preserve the nation's natural resources. In foreign policy, he focused on Central America, where he began construction of the Panama Canal. Roosevelt expanded the Navy and sent the Great White Fleet on a world tour to project American naval power. His successful efforts to broker the end of the Russo-Japanese War won him the 1906 Nobel Peace Prize. 