- Fighting should only be with enemy combatants, not with civilians. However it has always been recognised, to use a horribly euphemistic phrase, that 'collateral damage' is inevitable, and civilians will be killed in the cross-fire and moreover in the effort to destroy the enemy's infrastructure. The bombing of Hiroshima was justified on the basis that it would shorten the Second World War, a justification which is possibly dubious on strict interpretation of the laws of war, even if true. Unfortunately civilian bombing campaigns seem to have become pretty much the accepted norm since.
- Allied to the above, combatants have a duty to identify themselves as such. Essentially this means wearing uniform as bearing arms openly. Provided they do so they have corresponding rights, including the right to prisoner of war status. Suicide bombers, even if authorised by a state who regards itself at war, which is usually not the case, therefore cannot be combatants. Mercenaries are not combatants and are not therefore entitled to prisoner of war status. Mercenaries involved in the Angolan War of Independence in the 1970s were tried and shot by firing squad after defeat and this was probably not a breach of the laws of war. Spies are also in a very difficult position as, by definition, they do not identify themselves. It is worth saying that having non-combatant status doesn't mean you are not entitled to a trial and have human rights, but this maybe more a theoritical than real position in the case of mercenaries and spies.
- Prisoners of war must conversely not be treated harshly or punished in any way.
- When a conflict has ended, persons who have committed or ordered any breach of the laws of war, may be held individually accountable through process of law. Hence the concept of 'war crimes'. There have of course been numerous examples of action for war crimes in the 20th and 21st century, starting with the Nuremberg trials and leading through to the Tribunal for Former Yugoslavia which has tried Milosovic (who died before the trial ended) and is currently trying Karadic. In 2002, the International Criminal Court was founded, although it has not been joined by the major players, China,India, USA and Russia. It has opened investigations into Uganda and Democratic Republic of Congo for alleged atrocities.
It is often said that history belongs to the victors and this could be said of law too. It is usually the victorious who apply the laws of war, retrospectively, to the vanquished. There are of course some exceptions such as the eventual if half-heartened prosecution by US authorities of its own soldiers involved in the My Lai massacre in South Vietnam (and more recently Abu Grahib, Iraq) but the general proposition is probably true.