The immense military operations of our civil war have familiarized, to a considerable extent, not only those connected with the armies, but the people generally with the systems on which military forces are organized and the methods of conducting war. Much has been learned in the past three years, and much accomplished in the improvement of tactics, internal organization, and the construction of all kinds of material. Civilians, who were well read in the history of former wars, and even professional military officers, were comparatively ignorant of all the numerous details necessarily incident to the formation and movement of armies. On account of the deficiency of practical information on these matters, the difficulties which arose at the commencement of the war, were, as it is well known, immense; but they were overcome with a celerity and energy absolutely unparalleled in the history of the world, and to-day we are able to assure ourselves with justifiable pride that in all essential particulars our armies are fully and properly organized, equipped, and provided for. We propose to exhibit in a few articles the methods by which these results have been accomplished--to present to readers generally the system of organization and the principles of operation existing in our armies--giving them such information as can be obtained only from actual thorough acquaintance with military life, or extended perusal of works on military art, as now understood among the leading civilized nations.