To fulfill the purposes noted above, the laws of war place substantive limits on the lawful exercise of a belligerent's power. Generally speaking, the laws require that belligerents refrain from employing violence that is not reasonably necessary for military purposes and that belligerents conduct hostilities with regard for the principles of humanity and
chivalry. However, because the laws of war are based on consensus (as the nature of international law often relies on self-policing by individual states), the content and interpretation of such laws are extensive, contested, and ever-changing. The following are particular examples of some of the substance of the laws of war, as those laws are interpreted today.
Declaration of war Section III of the
Hague Convention of 1907 required hostilities to be preceded by a reasoned
declaration of war or by an ultimatum with a conditional declaration of war. Some treaties, notably the
United Nations Charter (1945) Article 2, and other articles in the Charter, seek to curtail the right of member states to declare war; as does the older
Kellogg–Briand Pact of 1928 for those nations who ratified it. These have led to fewer modern armed conflicts being preceded by formal declarations of war, undermining the objectives of the Hague Convention.
Lawful conduct of belligerent actors Modern laws of war regarding conduct during war (
jus in bello), such as the
1949 Geneva Conventions, provide that it is unlawful for belligerents to engage in combat without meeting certain requirements. Article 4(a)(2) of the
Geneva Convention relative to the Treatment of Prisoners of War recognizes Lawful Combatants by the following characteristics: • (a) That of being commanded by a person responsible for his subordinates; • (b) That of having a fixed distinctive sign recognizable at a distance; • (c) That of carrying arms openly; and • (d) That of conducting their operations in accordance with the laws and customs of war. Impersonating enemy combatants by wearing the enemy's uniform is possibly allowed, however the issue is unsettled. Fighting in that uniform is unlawful
perfidy, as is the taking of
hostages. Combatants also must be commanded by a responsible officer. That is, a commander can be held liable in a court of law for the improper actions of their subordinates. There is an exception to this if the war came on so suddenly that there was no time to organize a resistance, e.g. as a result of a
foreign occupation.
Persons parachuting from an aircraft in distress Modern laws of war, specifically within
Protocol I additional to the 1949 Geneva Conventions, prohibits attacking persons parachuting from an aircraft in distress regardless of what territory they are over. Once they land in territory controlled by the enemy, they must be given an opportunity to surrender before being attacked unless it is apparent that they are engaging in a hostile act or attempting to escape. This prohibition does not apply to the dropping of
airborne troops,
special forces,
commandos,
spies,
saboteurs,
liaison officers, and
intelligence agents. Thus, such personnel descending by parachutes are legitimate targets and, therefore, may be attacked, even if their aircraft is in distress.
Red Cross, Red Crescent, Magen David Adom, and the white flag (French:
Comité international de la croix-rouge) Modern laws of war, such as the 1949 Geneva Conventions, also include prohibitions on attacking
doctors,
ambulances or
hospital ships displaying a
Red Cross, a
Red Crescent,
Magen David Adom,
Red Crystal, or other emblem related to the
International Red Cross and Red Crescent Movement. It is also prohibited to fire at a person or vehicle bearing a
white flag, since that indicates an intent to surrender or a desire to communicate. In either case, persons protected by the Red Cross/Crescent/Star or white flag are expected to maintain neutrality, and may not engage in warlike acts. In fact, engaging in war activities under a protected symbol is itself a violation of the laws of war known as
perfidy. Failure to follow these requirements can result in the loss of protected status and make the individual violating the requirements a lawful target. ==Applicability to states and individuals==