An assassin’s bullet killed William McKinley and made Theodore Roosevelt the 26th president of the United States, the youngest in American history. It was a new era in America and the world, with the rise of technology and industry and an expanding role for the president in relation to Congress. Roosevelt took charge in regulating big business, passing laws to protect food and drugs, creating national parks and developing America’s military might—issues that will seem familiar to today’s young readers. Marrin offers another encyclopedic volume on a pivotal American leader and the time period, portraying him as a moral leader with an exuberance to match the spirit of his times. Long stretches of dense text are unrelieved by illustrations, though the many photographs—including some by Lewis Hine and Jacob Riis—and the well-chosen cartoons yield an interesting parallel narrative. Source notes are thorough, though there’s nothing to guide young readers to the wealth of other material available for them. A comprehensive resource for young researchers. (index) (Nonfiction. 12+)