General. - Among civilized nations the conduct of war is regulated by certain well-established rules known as the rules or laws of war. These rules cover and regulate warfare both on land and sea. Those which pertain particularly to war on land are called the rules of land warfare. It is the latter with which this manual is concerned.

    Written rules. - Many of the rules of war have been set forth in treaties or conventions to which the United States and other nations are parties. These are commonly called the written rules or laws of war.

    Unwritten rules. - Some of the rules of war have never yet been incorporated in any treaty or convention to which the United States is signatory. These are commonly called the unwritten rules or laws of war, although they are well defined by recognized authorities on international law and well established by the custom and usage of civilized nations.

    Basic principles. - Among the so-called unwritten rules or laws of war are three interdependent basic principles that underlie all of the other rules or laws of civilized warfare, both written and unwritten, and form the general guide for conduct where no more specific rule applies, to wit:

    Force of rules. – a. The unwritten rules are binding upon all civilized nations. They will be strictly observed by our forces, subject only to such exceptions as shall have been directed by competent authority by way of legitimate reprisals for illegal conduct of the enemy.       ( See par. 358.)

b. Technically each of the written rules is binding only between powers that have ratified or adhered to, and have not thereafter denounced (withdrawn from), the treaty or convention by which the rule is prescribed, and is binding only to the extent permitted by the reservations, if any, that have accompanied such ratification or adherence on either side. However, the written rules herein quoted in bold-faced type .are all prescribed by treaties or conventions each of which has been ratified without reservation, and not thus far denounced, by the United States and many other nations. They are in large part but formal and specific applications of general principles of the unwritten rules. While solemnly obligatory as between the signatory powers, they may be said also to represent the consensus of modern international public opinion as to how belligerents and neutrals should conduct themselves in the particulars indicated. As a general rule they will be strictly observed and enforced by United States forces in the field, as far as applicable there, without regard to whether they are legally binding upon all of the powers immediately concerned. It is the responsibility of higher authority, as occasions arise, to determine and to instruct the commander in the field, which, if any, of the written rules herein quoted are not legally binding as between the United States and each of the other powers immediately concerned, and which, if any, for that reason are not for the time being to be observed or enforced.

    Military government and martial law distinguished. - Military government is that form of government which is established and maintained by a belligerent by force of arms over occupied territory of the enemy and over the inhabitants thereof. In this definition the term "territory of the enemy," includes not only the territory of an enemy nation, but also domestic territory recovered by military occupation from rebels treated as belligerents.

    Martial law is the temporary government of the civil population through the military forces as necessity may require in domestic territory as distinguished from occupied territory of an enemy recognized as a belligerent.

    So far as the United States forces are concerned, military government and martial law are exercised by the military commander under the direction of the President, as Commander in Chief of the Army and Navy.

    The most prominent distinction between military government and martial law is, that the former is exercised only in the territory of a hostile belligerent and is within the realm of international law, while the latter is invoked only in domestic territory whose local government and inhabitants are not treated or recognized as belligerents.