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What is legal in war?

Residential building in Kyiv hit by a Russian missile. Photo: Julia Rekamie/Unsplash

What are the rules of war? Aren’t wars always illegal? What happens if someone breaks these rules? We asked Albert Vlodder, a doctoral student of law at Åbo Akademi University, to explain.

“The rules of war, also known as international humanitarian law (IHL) or the law of armed conflict, are the treaties and customs that states and individuals must abide by during armed conflicts.

Recognized principles such as military necessity, distinction, and proportionality influence these laws. They are primarily separated into two categories: the laws that govern when a state may use force to start a war (jus ad bellum) and the laws that govern the conduct during a war (jus in bello). The rules aim to reduce the consequences war can produce as much as possible.”

How did they come about?

“Generally, these rules were born from the experiences and developments of the numerous wars and battles throughout history. Much of our modern rules of war, such as those found under the United Nations Charter and the Geneva Conventions, were signed after World War II out of the necessity and desire of the international community to prevent and punish the types of atrocities, such as the Holocaust, from occurring again. Crimes such as genocide did not exist in name, let alone treaties, before the War.

During the famous Nuremberg Trials and Tokyo Trial, there was much debate on whether individuals could be charged with violating crimes established after they were committed. So, this intensified the need to have prohibitions against these horrible acts codified under international law.”

Aren’t wars, by definition, illegal? Is it possible to fight a legal war?

“Under Article 2 of the United Nations Charter, threatening or using force against another state is unlawful. In that sense, it is possible to say that under international law, war is illegal. However, the Charter provides two exceptions to the prohibition of force: in self-defence (individual or collective) of an actual or imminent armed attack or when authorized by the United Nations Security Council. So, under these conditions, it is possible to use force or fight in a war legally.

Another possible exception, which is controversial and contrary to the UN Charter, is to intervene through force on humanitarian grounds. An example of this is NATO’s involvement in the Kosovo War.”

What happens when someone breaks the laws of war?

“States and international courts investigate war crimes. Anyone, from civilians to military members and even heads of state, can be prosecuted.

States must investigate and prosecute individuals who, under their jurisdiction, violate the laws of war. Many states have incorporated these as crimes under national legislation and prosecute those who may have committed crimes elsewhere. We have seen this recently in Finland with the trial of a suspected former high-ranking Sierra Leone rebel group member who was found guilty of war crimes and then recently acquitted on appeal.

Crimes such as genocide did not exist in name, let alone treaties, before the War.

The International Criminal Court (ICC) is a permanent court located in The Hague, which can investigate, prosecute, and penalize perpetrators of the international crimes of genocide, war crimes, crimes against humanity, and a war of aggression. The United Nations Security Council also can establish war crime tribunals, such as in the conflicts of Yugoslavia and Rwanda. It is at these international courts where individuals can also be brought to justice when states are unable or unwilling to do so.”

Will anyone be held accountable for possible war crimes committed in, for example, Ukraine, Palestine or Yemen? If so, when?

“There is a great desire to have individuals who have committed these awful acts we see and hear about in the media be brought to justice. Early last year, the ICC issued two arrest warrants against individuals from Russia, including President Vladimir Putin, for the war crimes of unlawful deportation and transfer of children. However, it is unlikely that he will be in The Hague to face the charges anytime soon. The ICC does not conduct trials in absentia and has no enforcement capability to carry out arrests. It is incumbent on states to cooperate with the arresting and transferring of individuals charged by the ICC. While Putin is in power, he will unlikely be turned over to the Court.

The ICC Prosecutor is also investigating and collecting evidence in Gaza. Palestine is a member state of the ICC. It is difficult to put a time frame on potential charges, as, like Ukraine, the conflict is still taking place. I would expect arrest warrants for some of the more ‘clear’ violations, such as the initial Hamas attack of October 7th, 2023, first, but it is difficult to predict. Along with the developments in the Ukraine conflict, I think there is room for optimism regarding the active involvement of the ICC. Although, it can feel slow, especially during a humanitarian crisis that seems to be worsening.

There is a great desire to have individuals who have committed these awful acts we see and hear about in the media be brought to justice.

The civil war in Yemen is a different story. The ICC does not have jurisdiction since Yemen and some of the more active states involved are not member states of the Court, and Yemen has not requested an ICC investigation, such as Ukraine did in 2014. There have been attempts through the UN to establish war crimes investigations, which have been voted down. Unfortunately, it will likely take a while for war criminals to be held accountable in this nearly decade-long and devastating conflict.

While these questions focused more on individual responsibility of the laws of war, there is also the state responsibility aspect. A state can be held responsible for its actions and be ordered to stop its use of force and pay reparations. Recently, South Africa brought a claim of genocide against Israel at the International Court of Justice (ICJ) for Israel’s actions in Gaza. The ICJ issued many provisional measures against Israel in the prevention of genocide, however, they stopped short of ordering a ceasefire.”


Albert Vlodder is a doctoral researcher at Åbo Akademi University. He has a Masters degree in International Law, and his doctoral research focuses on the Law of the Sea and Maritime Law. Before pursuing a legal career, he served in the Royal Canadian Navy.