This brief history of the world’s greatest war(First World War/World War One) was prepared upon the suggestion of the National Board for Historical Service. Its purpose is to expand into an historical narrative the outline of the study of the war which the authors prepared for the Board and which was published by the United States Bureau of Education as Teachers’ Leaflet No. 4, in August, 1918. The arrangement of chapters and the choice of topics have been largely determined by the various headings in the outline for the course in grades seven and eight. The authors trust that the simple presentation here given may aid in developing a national comprehension of the issues involved in the war; and they hope it may play some part in preparing the American people for the solution of the great problems which lie immediately before us.