What is a war crime, and who gets held accountable? Here's what you need to know

The ongoing conflict between Israel and Hamas has led to accusations of war crimes on both sides, after Israeli civilians were targeted in Hamas' Oct. 7 attack and Israel responded with airstrikes on the densely populated Gaza Strip.

Under these conditions, protecting civilians can prove difficult or impossible. But combatants are bound by international humanitarian law to minimize the impact on populations.

Here's what to know.

In war, what are the obligations of nations, their soldiers and groups such as Hamas?

Although the history of international law regulating warfare goes back to the first Geneva Convention of 1864, World War II — in which twice as many civilians as fighters were among the tens of millions killed and the Nuremberg Trials that held Nazi leaders to account for atrocities — spawned interest in expanding the scope of the agreement.

The 1949 Geneva Convention established Article 3, delineated combatants from noncombatants and set down the obligations of governments and militaries on how to minimize casualties and the suffering of civilians in wartime.

International humanitarian law "basically grounds the parties to a conflict," says Fernando Travesí, executive director of the New York-based International Center for Transitional Justice, which works with victims of massive human rights violations. Armies, he says, have the right to go to war, "but that exercise of violence has limits."

The Geneva Convention has been agreed to by 196 states and serves as the international standard on the treatment of civilians, as well as prisoners of war and sick and wounded soldiers.

In a practical sense, every government in the world subscribes to these rules, says Kenneth Roth, a visiting professor at Princeton's School of Public and International Affairs and former executive director of Human Rights Watch. "I think it's important to stress that these [rules] are not the concoctions of human rights groups. These are not idealistic, pacifist rules. These are the rules that the militaries themselves adopted for themselves," he says.

Who can be held accountable under international humanitarian law?

A violation of protections under the Geneva Convention, such as the prohibition against deliberately targeting civilians, opens up leaders and common soldiers alike to prosecution. Such prosecutions could be handled by an international court or tribunal, or any nation exercising "universal jurisdiction" — a principle that allows any country's courts to prosecute war crimes.

Universal doctrine applies equally to Israel and Hamas, the militant group that governs the Gaza Strip, as well as Islamic Jihad, a small extremist group that has also carried out attacks against Israel.

Israel, like the United States and Russia, is not among the 123 states that are party to the Rome Statute, which established the International Criminal Court in The Hague, Netherlands. The Palestinians, however, joined in 2015, so the ICC has jurisdiction over the West Bank and Gaza Strip.

"That means that any Palestinian national can be prosecuted," Roth says.

And, he adds, it also means that any Israeli war crime committed inside Palestinian territory can also be prosecuted.

A United Nations-established body known as the Independent International Commission of Inquiry on the Occupied Palestinian Territory, including East Jerusalem and Israel, says it has begun "collecting and preserving evidence of war crimes committed by all sides" since the start of the conflict following the Hamas attacks.

On Friday, Amnesty International said it had documented evidence that Israeli forces were failing to discriminate between military targets and civilians. It also called on Hamas to release civilian hostages and immediately end indiscriminate rocket fire.

What constitutes a war crime?

Civilians inevitably get caught between warring parties, but the norms of international humanitarian law require that "you never target civilians, you never indiscriminately fire on a civilian area, you never launch an attack that will have a disproportionate impact on the civilian population," according to Roth.

"Premeditated, planned and deliberate killing of civilians — that's a clear war crime," the ICTJ's Travesí says.

By that definition, he says, the Oct. 7 attack by Hamas that targeted Israeli civilians, killing some 1,400, clearly fits within the definition of a war crime. Hamas militants took about 200 others hostage — an act also explicitly prohibited by the Geneva Convention.

Despite Hamas being an irregular force, it is subject to the same international humanitarian law as Israel Defense Forces soldiers, says Oona Hathaway, a Yale Law School professor and founder and director of the school's Center for Global Legal Challenges.

"International humanitarian law applies not just in conflicts between states ... between ... a modern sovereign state and another sovereign state, but also between states and nonstate actors," she says. "So here we've got a conflict between Hamas, which is a nonstate actor group, and a state that is Israel."

And Hamas' attacks, brutal killings and kidnapping of Israelis, clearly constitute war crimes, says Hathaway, coauthor of The Internationalists: How a Radical Plan to Outlaw War Remade the World.

Civilians often find themselves in the wrong place at the wrong time — near, for example, what is presumed by combatants to be a legitimate military target. Those cases can be a gray area for military decision-makers and in international humanitarian law, where the principle of proportionality applies.

An attack would not be proportional "if the civilian injury, civilian death or damage to civilian objects expected from such an attack would be excessive in relation to the concrete and direct military advantage anticipated from that attack," explains Tom Dannenbaum, associate professor of international law at the Fletcher School at Tufts University.

"That's obviously a complicated process and is often subject to debates about exactly when that line is crossed," he says.

The densely populated Gaza Strip presents "a huge challenge" for the Israeli military, Travesí acknowledges. Fighting an irregular force such as Hamas, whose fighters operate in urban areas and don't wear uniforms, makes that challenge even more difficult, says Roth.

"It can be difficult for the attacker to distinguish between a combatant and a noncombatant. But that difficulty does not absolve the attacking party from the duty always to distinguish between combatants who can be targeted and noncombatants who cannot be," Roth says.

In recent days, Israel Defense Forces told Gazans to evacuate the north of the territory during an apparent ramped-up bombardment in retaliation for Hamas' attack on Israel, and in anticipation of an expected ground assault.

That could be seen as a humanitarian gesture, "but it has been done in a wholly inhumane way, because to order 1.1 million people to evacuate in the course of a few hours is obviously impossible," Roth says. "It's cruel, [and] it creates panic."

Preventing or withholding medical supplies and medical care for civilian population "could amount to a war crime as well, because that could amount to a collective punishment," which is also a violation of the Geneva Convention, according to Travesí.

And simply warning the population to leave to avoid further harm does not allow a military force to wash its hands of responsibility, Dannenbaum notes.

"Whether or not individuals comply with that warning does not change their status," he says. "So if they don't move, if they remain in that location, their civilian status endures and has precisely the same weight in the context of proportionality as it would have absent the warning."

How can war crimes be prosecuted?

Simply gathering evidence of war crimes can be extremely difficult amid the fog of war, Travesí says.

"That's why many, many human rights activists and many journalists, they collect a lot of documentation and evidence that might be very, very important for the future or accountability processes," he says.

Suspects can be brought before the International Criminal Court at The Hague or ad hoc tribunals, or at the national level, something that the ICC encourages, Dannenbaum says.

"It defers to genuine national prosecutorial efforts. In this way, it's different from the former Yugoslav and Rwanda tribunals, which had primary jurisdiction. So the International Criminal Court actually encourages national governments to prosecute their own offenders."

In 1961, Israel itself, for example, famously exercised universal jurisdiction to try Nazi officer Adolf Eichmann for his role in the Holocaust and war crimes committed during World War II. That trial was broadcast around the world.

However, justice at the international level can be slow, complex — and frequently unsatisfying.

"In any conflict in the world, you can't have the expectation that you will prosecute everybody," Travesí says. "So, you have to choose some. You have to do some selection and prioritization of cases."

In other words, top leaders may be held accountable for war crimes, while rank-and-file soldiers are able to evade justice.

When it comes to bringing prosecutions of war crimes, "The ICC has not had a high success rate," Dannenbaum acknowledges.

Even so, an international arrest warrant could be executed by any of the 123 ICC member nations. Indeed, they would be required to do so. The accused, Dannenbaum says, "would take a significant risk in traveling" to any member state.

"That's the reason that [Russian President] Vladimir Putin did not travel to South Africa for the BRICS summit this summer," he says, referring to the international meeting of emerging economies that took place in Johannesburg in August. "South Africa would have had an obligation to arrest him, because there was an arrest warrant from the ICC — and South Africa is an ICC state party."

Copyright 2023 NPR. To see more, visit https://www.npr.org.