Though the New Criticism had its origins in Britain in the criticism of T. S. Eliot, the theory of I. A. Richards and the practice of William Empson, its most powerful impact has been in America. John Crowe Ransom, who published a book entitled The New Criticism in 1941, was the leading American influence and he acknowledged a debt to Eliot and Richards. The other major American New Critics were Cleanth Brooks, Allen Tate, Robert Penn Warren and W. K. Wimsatt. Indirectly related to the New Criticism are such important figures as Kenneth Burke and R. P. Blackmur. The early New Critics were politically conservative and their attitudes to literature were shaped by their opposition to certain twentieth-century tendencies of thought, such as Marxism.