In republishing these essays in collected form, it has seemed best to issue them as they were originally printed, with the exception of a few slight corrections of slips in the text and with the...

 In republishing these essays in collected form, it has seemed best to issue them as they were originally printed, with the exception of a few slight corrections of slips in the text and with the omission of occasional duplication of language in the different essays. A considerable part of whatever value they may possess arises from the fact that they are commentaries in different periods on the central theme of the influence of the frontier in American history. Consequently they may have some historical significance as contemporaneous attempts of a student of American history, at successive transitions in our development during the past quarter century to interpret the relations of the present to the past. Grateful acknowledgment is made to the various societies and periodicals which have given permission to reprint the essays.