text: General Background and Basic Principles of the Law of Armed Conflict
  law does not prevent a State from punishing its nationals whom it may capture among the ranks of enemy
  forces. For example, under U.S. law, not only may U.S. nationals who join enemy forces be subject to attack
  or detention by U.S. forces, they may also be tried for treason (18 U.S.C. § 2381).
  CIVILIANS
  1-54. In general, a civilian is a member of the civilian population—that is an individual who is neither part
  of nor associated with an armed force or group, nor otherwise engaging in hostilities. For example, any person
  who belongs to any of the combatant categories referred to in GPW Article 4(A)(1), (2), and (3) (these
  categories are discussed in paragraphs 3-16 to 3-25), are not civilians. For most purposes, the term “civilian”
  does not include unprivileged belligerents.
  1-55. Like combatants, members of the civilian population also have certain rights, duties, and liabilities
  under LOAC. Civilians may not be made the object of attack, and feasible precautions must be taken to
  reduce the risk of harm to them. Civilians are generally treated consistent with the GC and many qualify for
  protections established for protected persons under the convention (GC art. 4). Civilians generally may be
  temporarily detained when militarily necessary and may be interned for imperative reasons of security. In all
  circumstances, they are entitled to humane treatment. Civilians lack the combatant’s privilege and may be
  punished by an enemy State for engaging in hostilities against it.
  Civilians and the Conduct of Hostilities
  1-56. Civilians who take a direct part in hostilities forfeit their protection from being made the object of
  attack (see DOD Law of War Manual, 5.8; consider AP I art. 51(3); AP II, art. 13(3)). Civilians might be
  killed incidentally in military operations; however, the principle of proportionality requires that the expected
  incidental harm to civilians may not be excessive in relation to the concrete and direct military advantage
  anticipated from an attack, and underlies the requirement that feasible precautions must be taken to avoid
  harming civilians during military operations. Private persons who join a non-State armed group or otherwise
  engage in hostilities forfeit the corresponding protections of civilian status and may be liable to treatment in
  one or more respects as unprivileged belligerents.
  Civilians and Detention
  1-57. In general, civilians may be subject to non-violent measures of control and security that are justified
  by military necessity, such as searches or temporary detention. Belligerents or Occupying Powers may take
  necessary security measures in relation to civilians, including internment or assigned residence for imperative
  reasons of security (GC arts. 42, 78). Civilians who are interned or confined to assigned residences during
  international armed conflict or occupation generally are classified as protected persons under the GC and
  receive a variety of protections. Chapter 5 addresses, in detail, the treatment of civilian internees during
  international armed conflict and occupation. In all circumstances, detained civilians must be treated
  humanely.
  Civilians’ Liability Under an Enemy State’s Domestic Law
  1-58. Unlike combatants, civilians generally lack any special immunity from the domestic law of the enemy
  State. Private persons who engage in hostilities or provide support to the enemy may be punished by an
  opposing State for their conduct pursuant to a conviction following a fair trial. Moreover, a State that is an
  Occupying Power has additional authority over enemy civilians that extend beyond the ability to punish their
  unauthorized participation in hostilities. Note, however, the special cases of diplomats, persons authorized to
  accompany the armed forces, members of the merchant marine, crews of civil aircraft, and participants in a
  levée en masse, who might have certain immunities from foreign domestic law.
  MIXED CASES
  1-59. Certain classes of persons do not fit neatly within the dichotomy of the armed forces and the peaceful
  civilian population, that is, combatants and civilians. These classes may be classified into three groups:
  certain humanitarian personnel; certain civilian supporters of the armed forces; and, unprivileged
  belligerents. Each of these classes has some attributes of combatant status and some attributes of civilian