Theodore Roosevelt’s presidency marked the beginning of United States imperialism. Matt Oyos explains how Roosevelt modernized the military to bolster America’s international presence. Also: Arthur Schlesinger Jr. was the foremost presidential historian of the 20th century. Over the course of his career, he won two Pulitzer prizes and was a close friend and advisor to former president, John F. Kennedy. Emile Lester says Schlesinger’s work can teach us a lot about what makes a successful liberal presidency.

Later in the show: What makes a leader decide to go to war? Is the decision based solely on facts on the ground or does it have something to do with personality? Dennis Foster and Jonathan Keller have developed a psychological framework for uncovering why leaders do the things they do.