Theodore Roosevelt became the youngest U.S. President in 1901 at age 42 after the assassination of William McKinley. As President, Roosevelt pursued progressive reforms and established himself as a trustbuster by taking on large corporations like Northern Securities Company in antitrust cases. He was a conservationist and established 150 million acres of national forests during his presidency. Roosevelt also oversaw the construction of the Panama Canal and earned a Nobel Peace Prize for mediating the end of the Russo-Japanese War. Though eligible, Roosevelt chose not to run for a third term in 1908, instead backing his friend William Howard Taft as the Republican candidate.