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.
Various essays dealing with the connection of diplomatic history and the frontier and others stressing the significance of the section, or geographic province, in American history, are not included in the present collection. Neither the French nor the Spanish frontier is within the scope of the volume.
The future alone can disclose how far these interpretations are correct for the age of colonization which came gradually to an end with the disappearance of the frontier and free land. It alone can reveal how much of the courageous, creative American spirit, and how large a part of the historic American ideals are to be carried over into that new age which is replacing the era of free lands and of measurable isolation by consolidated and complex industrial development and by increas-