Herbert Croly, founder and editor of the New Republic, was a prophet of the liberal political faith. He refined and crystallized much of the thinking behind the Progressive movement in The Promise of American Life (1909), an astute, timely book that was at once programmatic, philosophical, and critical. Consequently, he was able to make the New Republic a small but significant national forum for primarily urban, eastern perspectives on politics and letters.

Croly was the only son of parents who were prominent polemicists and journalists. His father, David Goodman Croly, worked as a New York Evening Post reporter in the 1850s before joining his wife in an ill-fated publishing venture with a Democratic newspaper in Rockford, Illinois. Returning to New York, he served as city editor and then as managing editor of the World during the Civil War. He edited and was a stockholder in the Daily Graphic from...