Colomb did not invent the term "sea-power", as it is of very ancient origin, nor did he employ it until Captain Mahan of the United States Navy had made it a household word with all. But he thoroughly grasped its conditions, and in his great work on "Naval Warfare" (first published in 1891) he enunciated its principles with great cogency and with keen historic insight. The central idea of his teaching was that naval supremacy is the condition precedent of all vigorous military offensive across the seas, and, conversely, that no vigorous military offensive can be undertaken across the seas until the naval force of the enemy has been accounted for either destroyed or defeated and compelled to withdraw to the shelter of its own ports, or at least driven from the seas by the menace of a force it dare not encounter in the open. This broad and indefeasible principle he enunciated and defended in essay after essay, in lecture after lecture, until what at first was rejected as a paradox came in the end to be accepted as a commonplace. He worked quite independently of Captain Mahan, and his chief conclusions were published before Captain Mahan's works appeared.