With the assassination of President McKinley, Theodore Roosevelt, not quite 43, became the youngest President in the Nation's history. During the Spanish-American War, Roosevelt was lieutenant colonel of the Rough Rider Regiment, which he led on a charge at the battle of San Juan. He was one of the most conspicuous heroes of the war. Roosevelt forced the dissolution of a great railroad combination in the Northwest. Other antitrust suits under the Sherman Act followed. Aware of the strategic need for a shortcut between the Atlantic and Pacific, Roosevelt ensured the construction of the Panama Canal and he even won the Nobel Peace Prize for mediating the Russo-Japanese War, reached a Gentleman's Agreement on immigration with Japan, and sent the Great White Fleet on a goodwill tour of the world.