To thank all who kindly assisted the author to obtain material is practically impossible; but a number of names appear in the list of MS. sources, and others must be mentioned here. Without the cordial support of Presidents Theodore Roosevelt and Porfirio Diaz, Secretary of State Elihu Root, Minister of Relations Ignacio Mariscal, and Senator Henry Cabot Lodge this history could not have been written; and the author acknowledges with no less pleasure his special obligations to Whitelaw Reid, American Ambassador to Great Britain, Joseph E. Willard, Ambassador to Spain; Henri Vignaux, First Secretary of our embassy at Paris; J. J. Limantour, Minister of Hacienda, Mexico; Major General J. Franklin Bell, Chief of Staff; Major General F. C. Ainsworth, Adj. Gen.; Admiral Alfred T. Mahan; Admiral French E. Chadwick; Brigadier General J. E. Kuhn, Head of the War College, Washington; Dr. J. Franklin Jameson, Director of the Department of Historical Research, Carnegie Institution; Dr. Gaillard Hunt, Chief of the Division of MSS., Library of Congress; Dr. St. George L. Sioussat, Brown University; Dr. Eugene C. Barker, University of Texas; Dr. Herbert E. Bolton, Professor Frederick J. Teggart and Dr. H. I. Priestley of the University of California; Dr. R. W. Kelsey of Haverford College; Dr. J. W. Jordan, Pennsylvania Historical Society; Dr. Worthington C. Ford, Editor for the Massachusetts Historical Society; Dr. Solon J. Buck of the Minnesota Historical Society; R. D. W. Connor, Secretary of the Historical Commission of North Carolina; Dr. R. P. Brooks of the University of Georgia; Dr. Dunbar Rowland, Director of the Archives and Historical Department of Mississippi; T. M. Owen, Director of the Historical Department of Alabama; Dr. George M. Philips, State Normal School, West Chester, Pa.; Waldo G. Leland, Secretary of the American Historical Association; W. B. Douglas and Miss Stella M. Drumm, Librarian, of the Missouri Historical Society; Dr. Clarence E. Alvord of the University of Illinois and Mrs. Alvord (formerly Miss Idress Head, Librarian of the Missouri Historical Society); Ignacio Molina, Head of the Cartography Section, Department of Fomento, Mexico; Charles W. Stewart, Librarian of the Navy Department; James W. Cheney, long the Librarian of the War Department; Major Gustave R. Lukesh, Director, and Henry E. Haferkorn, Librarian of the United States Engineer School, Washington Barracks; D. C. Brown, Librarian of the Indiana State Library; Victor H. Paltsits, Department of MSS., New York Public Library; W. L. Ostrander of the library at West Point; Lieutenant James R. Jacobs, 28th United States Infantry; Dr. Katherine J. Gallagher; Dr. Martha L. Edwards. To the widow of Admiral Charles S. Sperry and their son, Professor Charles S. Sperry, the author is particularly indebted for an opportunity to examine important papers left by William L. Marcy. Valuable suggestions were most kindly given by Dr. William A. Dunning of Columbia University and Dr.