Curious Kids is a series for children of all ages. If you have a question you’d like an expert to answer, send it to curiouskidsus@theconversation.com.

What are war crimes and when did they start? – Artie, 12, Queens, New York

I imagine you’re asking about “war crimes” because you’ve heard that term mentioned lately in news about the conflicts underway in Gaza, Ukraine and Sudan. The idea may sound confusing, because war always includes killings and destruction. But special rules restrict how wars can be fought.

I am a professor who studies international law – the set of rules that defines what a war crime is.

Why do we need laws about war?

Historically, war had few limits. Individual societies occasionally attempted to control how wars were fought. But for much of human history, when nations attacked each other, it wasn’t just soldiers who died. Many civilians – ordinary people who weren’t fighting in the war – died, and whole cities were destroyed.

After wars ended, survivors from the losing country might even end up as slaves taken back to the victorious country.

There were no “laws of war” that restricted conquests by the Egyptians and Romans in ancient times between 600 and 30 B.C. No laws limited the Mongol invasions of Europe in the 13th century or the European colonial invasions of Latin American, African and Asian societies in the 18th through 20th centuries.

Even as recently as the 1940s, during World War II, U.S. and U.K. forces killed hundreds of thousands of people in their bombings of German and Japanese cities. Nazi Germany systematically murdered approximately 6 million Jews and others during the Holocaust.

When did war get laws?

There is no supreme world government that can create laws for all countries, so international law is formed by rules that countries agree to respect. These are called treaties.

In the 19th century, countries and many private groups worldwide began working to develop the laws of war.

Early treaties on war were meant primarily to protect soldiers from unnecessary pain and suffering. Countries agreed to stop using really dangerous weapons such as poison gas, for example. They also banned murdering wounded enemies and soldiers who tried to surrender, because those killings aren’t necessary to win a war.

Later, after the horrors of World War II, the laws of war were expanded to protect civilians.

Developing all these rules has taken well over a century. Nations agreed to them because everyone has a shared interest in limiting some of the worst aspects of how war is fought. The goal is to keep everyone caught up in war as safe as possible, while accepting that some innocent people will still die.

What are war crimes?

The rules of war are set out primarily in four treaties from 1949 called the Geneva Conventions. Every country in the world accepts these rules, which have been expanded several times in the years since.

The Geneva Conventions are very specific about what warring nations cannot do during an armed conflict. The things they cannot do are called war crimes.

Here is a partial list of war crimes:

• Deliberate killing that is not justified by a legitimate military objective.
• Torture.
• Inflicting severe harm on enemies.
• Taking hostages.
• Wounding or killing a soldier who has surrendered.
• Attacking civilians not participating in the conflict.
• Using certain prohibited weapons.
• Starving people as a weapon of war.

How are war crimes punished?

Most people generally agree that these are good rules and that warring countries should try to obey them. The problem is enforcement.

War crimes are committed not by entire countries but by individual people, such as soldiers who torture the captured enemy or destroy a family’s crops unnecessarily. Since individuals commit the crimes, individuals must be held responsible.

Many countries have laws stating what can and cannot be done during war. They generally reflect the rules of the Geneva Conventions. However, history shows that governments are often reluctant to prosecute their own soldiers for war crimes. Accusations of such crimes are often ignored, punished lightly or dismissed.

That’s why the International Criminal Court exists. In 1998, representatives from 160 countries met in Rome to create this world court, which can investigate, bring to trial and decide the guilt or innocence of individuals accused of war crimes and certain other international crimes.

Today, 124 countries have accepted the court’s authority. If war crimes are committed in these countries, the court can act. In 2014, for example, the head of a rebel force in the Democratic Republic of Congo was convicted of murder and deliberately attacking civilians; he was put in prison for 12 years.

However, several big and powerful countries have not consented to the authority of the International Criminal Court, including the United States, China and Russia. Many countries in which brutal wars have occurred also reject its powers, including Iraq, Israel, Syria, Sudan and Yemen. This limits its powers.

Additionally, the International Criminal Court has no international police force to arrest suspects. It relies on governments to detain people accused of war crimes and deliver them to the court.

Again, not all of them cooperate. National leaders have sometimes traveled abroad after International Criminal Court arrest warrants were issued against them and have not been arrested.

Finally, interpreting international law can be tricky.

It is a war crime to deliberately attack civilians, but countries at war with each other still bomb apartment buildings, hospitals and schools sometimes, claiming enemy forces are inside those buildings. If true, that could make the buildings legitimate military targets – though international law still requires militaries to do everything possible to minimize civilian casualties.

What next?

Right now, you may be thinking: If people aren’t punished for breaking the rules of war, do these rules even matter?

It’s a reasonable question. But consider this: Countries have had criminal laws against murder and robbery for thousands of years, yet these crimes are still committed. The concept of war crimes has been around for a much shorter time. It is not surprising that not all war criminals can be brought to justice, but I think the fact that most countries now agree that war crimes should be prohibited is important.

Plus, when war crimes are investigated and condemned, victims may feel that their suffering will not be forgotten. Even if no one is punished, proving a crime was committed has value.

International law isn’t easy to enforce, but at least most of the world now recognizes that even wars must have their limits.

Hurst Hannum does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.