"O'Har" (2006) shows that in his classic interdisciplinary history of the post-Civil War West, Webb develops dominant characteristics of the Great Plains – treelessness, level terrain, and semiaridity – and examines effect on the lives of people from very different environments. To succeed, pioneers made radical readjustments in their way of life, eschewed traditions, and altered social institutions. Webb believed what set the Great Plains apart from other regions was its individualism, innovation, democracy, and lawlessness, themes he derived from the Frontier Thesis of Frederick Jackson Turner. His focus is said to have missed the emergence of a national empire, and others criticize him for failing to acknowledge the roles played by women, Indians, and Mexicans.