It is perhaps almost superfluous for me to say that it would have been impracticable for me within the limits of these two volumes to give an account of every debate in Congress in which Mr. Buchanan took part, or of every transaction with which he was connected as a foreign minister, as Secretary of State, or as President. Such of his speeches as I have quoted at length have been selected because of the interest that still attaches to the subject, or some part of it, or because they illustrate his powers as a debater; and in making selections or quotations from his diplomatic papers, I have been unavoidably confined to those which related to critical questions in our foreign relations. It was equally impracticable for me to touch upon the connections which he had with numerous political persons in the course of a public life of forty years. I have drawn a necessary line, and have drawn it between those with whom he stood in some important official relation, or who occupied important public positions, and those who belong in the category of politicians more or less prominent and active, with whom all very eminent public men have more or less to do; including the former and excluding the latter. But of course I have varied this rule in the case of friends who stood in personal rather than political relations with him.
It remains for me to give a description of the materials of which I have made use, and to make the customary acknowledgments to those who supplied them.
Any man who has been in public life for a long period of time, and has attained to the highest public stations, must necessarily have accumulated a vast amount of materials of the highest importance to the elucidation of his own history and of the history of the times in which he has acted. Mr. Buchanan had a habit of preserving nearly everything that came into his hands. The mass of his private correspondence is enormous. I can hardly specify the number of letters that I have had to read, in order to form an adequate idea of the state of the public mind in the opposite sections of the Union during the period when he first had to encounter the secession movement. My recollection of the condition of public opinion at such junctures was pretty vivid, but I could not venture to trust to it without examining the best evidence; for undoubtedly the best evidence of public opinion was to be found in the private letters which at such periods reached the President from all quarters of the country. Many hundreds of such letters have been examined, in order to write, and to write correctly, a very few pages. Mr. Buchanan had also another habit of great utility. Although he did not always keep a regular diary or journal, he rarely held an important conversation, or was engaged in a critical transaction, without writing down an account of it with his own hand immediately afterward. These extremely valuable memoranda will be found to throw great light upon many matters that have hitherto been left in obscurity, or have been entirely misrepresented. He was also an indefatigable letter-writer; and of those of his own letters of which he did not keep copies, he procured many from his correspondents after his retirement to Wheatland. He wrote freely, easily, and I should think rapidly. His familiar letters rarely received or required much correction; but his official productions were polished with great care.