Eugene H. Berwanger's study of anti-slavery sentiment in the antebellum West is as resoundingly important now, in a new paperback edition, as when first published in 1967. In The Frontier against Slavery, Berwanger attributes the social and political climates of the states and territories Ohio River Valley pioneers settled before 1860 to racial prejudice.   Drawing from newspaper accounts, political speeches, correspondence, and legal documents, Berwanger reveals that the whites-only sentiments of the pioneers, rather than humanitarian concern for African Americans, limited the expansion of slavery. This whites-only prejudice shaped laws in the majority of western states and territories that excluded all African Americans, enslaved or free, from citizenship, evidencing the deep-rooted discrimination of political leaders and pioneers.