The lectures delivered at the Naval War College were the basis of “The Influence of Sea Power upon History.” The author tells us how the central idea came to him in the library of the English Club at Lima, Peru, while reading Momsen’s “History of Rome.” “It suddenly struck me ... how different things might have been could Hannibal have invaded Italy by sea, as the Romans often had Africa, instead of by the long land route.” A year later, when he returned to the United States, the plan of the lectures was already formed: “I would investigate coincidently the general history and the naval history of the past two centuries with a view to demonstrating the influence of the events of the one upon the other.” Written between May and September of 1886, and delivered as lectures during the next four years, the book was carefully revised before its publication in the spring of 1890. This book exerted at the time, and has continued to exert, a widespread influence; and while its author’s reputation has been increased by his later writings, it remains his best known and greatest work. One reason for this is that it states his fundamental teaching, and in a form easy to grasp. The preface and the first chapter, which cover but eighty-nine pages, survey rapidly the rise and decline of great sea powers and the national characteristics affecting maritime development. The rest of the book, treating in detail the period between 1660 and 1783, reinforces the conclusions already stated. Timeliness also contributed to its success. The book furnished authoritative guidance in a period of transition and new departures in international affairs. For nearly twenty years, under Bismarck, Germany had been consolidating the empire established in 1871. When William II ascended the throne in 1888, the ambitions of both ruler and nation were already turned toward colonial expansion and world power. A German Admiralty separate from the War Office was established in 1889; Heligoland was secured a year later; the Kiel Canal was nearing completion. In England, the Naval Defense Act of 1889 provided an increase of seventy ships during the next four years. The rivals against whom she measured her naval strength were still France and Russia. In the United States, Congress in 1890 authorized three battleships, the first vessels of this class to be added to the American navy. During the following ten years the rivalry of nations was chiefly in commercial and colonial aggrandisement, marked by the final downfall of Spain’s colonial empire and a greatly increased importance attached to control of the sea.