Reading the United Nations charter, you might be forgiven for thinking that wars have been scrapped. Article 2 says that no country shall use force or the threat of force against "the territorial integrity or political independence of any State".
But in Article 51, it goes on to say that states do have the right to self-defence if an armed attack occurs against them.
In the past, people talked about a 'just war'. Today, they are more likely to use the words 'legitimate use of force'. But the principle is the same, and almost always means self-defence.
Talk about the threat of war against Saddam Hussein's Iraq. Some argue that self-defence against a possible attack justifies a US-led attack. Others disagree. Why? What do young people think?
Separate from the justice of the causes of a war is its conduct. It does not matter who started it - all parties to a war are bound by what is called international humanitarian law. Part of this is the Geneva Convention, which lays down rules about treating prisoners, the sick and wounded, and protecting civilians.
The laws of the Hague Tribunal, a panel of arbitrators for international disputes, say how wars should be fought and what weapons can be used.
For example, bullets that explode on impact are outlawed, as are laser weapons that blind enemy soldiers. Targeting civilians is a war crime.
The International Court of Justice can try those suspected of war crimes, genocide and crimes against humanity.
If you talk about war, watch for signs of distress. Young people may have generalised worries. Some will also have specific fears if they have a parent, relative or friend in the Forces or family ties in Iraq.
There could also be young armchair generals, who treat war like a large-scale video game. You may want to be ready to challenge any such indifference to the real horrors of war.
