Wikipedia Commons: 1, 3, 5, 6, 9, 11, 13, 22, 30, 37
Wikipedia Commons (Courtesy Museum of Fine Arts, Boston): 2
Museo Centrale del Risorgimento: 4
Library of Congress: 7, 17, 19
Wikipedia Commons (Courtesy of U.S. Department of the Interior): 8
German Federal Archives: 10, 14, 18, 20
Courtesy of Elan Steinberg: 12
Collezione Cartoline Albertomos: 15
© Bettmann/CORBIS: 23, 25, 26, 34, 36
© Corbis: 24
© Gianni Giansanti/Sygma/Corbis: 27
AP/Raul Fornezza: 32
© Andrzej Grygiel/epa/Corbis: 38
© KNA-Bild/dpa/Corbis: 39
© Gianni Giansanti/Immaginazione/Corbis: 40
Author photo of Vanity Fair cover: 41
© Stringer/Italy/Reuters/Corbis: 42
AP Photo/El Salvador School: 43
Author photo of Time cover: 44
© Alessandro Bianchi/Reuters/Corbis: 45