Editor’s note: Mary Ellen O’Connell is the Robert and Marion Short professor of law and professor of international peace studies-Kroc Institute at the University of Notre Dame. She is the co-author of “Self-Defense Against Non-State Actors” (2019), among many other publications. The views expressed in this commentary are the author’s own. View more opinion at CNN.
Hamas’ massive, brutal attacks and kidnappings perpetrated against Israelis on October 7 violated humanity’s most fundamental international legal principles. Those same principles govern Israel’s right of response, and they are best fulfilled through an immediate ceasefire by all parties, not an Israeli ground offensive in Gaza.
International law is the law that governs all relations at the interstate level. It is thus the law clearly relevant to the Israel-Hamas conflict.
Within international law, two sets of rules have particular application. They are human rights and the law governing the use of force, which consists of both rules on resorting to armed force and the rules on the conduct of force, also known as the law of armed conflict, the law of war or international humanitarian law.
International human rights law is found in widely adopted treaties and protects such basic rights as the right to life and freedom from arbitrary detention. It requires that Hamas cease its fire and release its hostages. There is also a well-established right under human rights law that permits Israel to use limited force to rescue nationals held by Hamas.
The most important international legal rule for the protection of human rights is the prohibition on the use of armed force in UN Charter Article 2(4). Human rights need peace to flourish, and Article 2(4) promotes peace by prohibiting the use of force outside a state’s territory, unless it is in self-defense, as permitted by Charter Article 51, when authorized by the UN Security Council or when invited by the government of a state.
In addition to the UN Charter, two rules of general international law also restrict resort to force. The principle of necessity requires that any force used — even in self-defense under Article 51 — be as a last resort and have a reasonable chance of accomplishing the lawful military objective.
If the requirements of necessity can be met, the principle of proportionality then mandates that the force used must be commensurate to the injury suffered. These principles have been applied by the International Court of Justice in case after case.
Some have compared Hamas to ISIS and argued Israel may fight Hamas as the United States fought ISIS. If the comparison is meant to provide a legal justification for attacking Gaza, it fails. First, Iraq issued a formal invitation to the US and other states to provide military assistance against ISIS on its own territory. The invitation was issued in a letter to the UN Security Council, which the US accepted. Israel has no such invitation to assist against militants in Gaza. And when the US pursued ISIS beyond Iraq into Syria, it refused to request an invitation from the Syrian government and therefore had no legal right to fight on Syrian territory.
Regardless of whether a state is resorting to force lawfully under the UN Charter, all use of force must follow the principles on the conduct of force. Laws on the conduct of force are codified in multiple, complex treaties, from the Geneva Conventions of 1949 to the statement of war crimes in the Rome Statute of the International Criminal Court. The most important norms are superior to treaties, binding all fighters in armed conflict. They allow no derogation and include the principles of civilian distinction, necessity, proportionality and humanity.
Civilian distinction forbids the intentional or indiscriminate targeting of civilians or those no longer taking part in fighting. Military necessity restricts targeting to legitimate military objectives, the destruction of which will provide a definite military advantage. Even then, targeting is unlawful if it causes a disproportionate loss of civilian lives.
Finally, regardless of the right to target under the rules just cited, mercy must always be shown as mandated by the principle of humanity — a normative principle that “seeks to limit suffering, injury, and destruction” and “precludes the assumption that anything that is not explicitly prohibited by specific (International Humanitarian Law) rules is therefore permitted.”
The protections to which civilians have a right under international law during armed conflict are almost impossible to respect in anti-terror wars, as Israel’s bombing of densely populated Gaza shows.
If there is any doubt about whether people are civilians or not, the presumption is that they have civilian status. Denial of food, water, medicine and other necessities to the civilian population is never permissible.
Hamas militants know they are putting innocent lives at risk and have as much responsibility as Israel to end their resort to force. They have a clear duty to release hostages. The cost to civilians in this conflict is so high that the principle of humanity demands an end to all fighting.
More than 175 US legal scholars have called on President Joe Biden to negotiate an immediate ceasefire, win the release of hostages and get emergency aid to the suffering population of Gaza — demands that are in compliance with international law.
While some aid shipments have entered Gaza at last, more is needed — and Biden has pressed this point both privately to Israeli Prime Minister Benjamin Netanyahu, and publicly by calling for humanitarian pauses (which Netanyahu rebuffed). But Biden has stopped short of calling for a ceasefire — which he should do immediately.
For many years, Israel has attacked Gaza persistently, and Hamas has consistently launched rockets attacks at Israel. Israel has conducted ground invasions, most recently in 2009 and 2014, with Hamas in each case emerging stronger than before.
While the current conflict began after Hamas’ attack on October 7, Israel’s past invasions have played a role in fueling the ongoing cycle of revenge and violence by Hamas and other Palestinian militants. Ron Dermer, Israel’s minister of strategic affairs and an observer of Israel’s war Cabinet, acknowledged the cycle of violence when he said, “We have to take action to make sure that this is not just another round, that this round is the last round.”
Israel is now trying to do that by seeking to destroy Hamas rather than weaken it — a goal that will require urban combat amid a vast underground tunnel system, while factoring in Palestinian civilians and Israeli hostages. Given these issues, it is difficult to see how Israel’s ground offensive has a reasonable chance of success (which is required by the principle of military necessity).
Then there are the risks of the war devolving into a wider regional conflict, and lingering issues of governance, should Israel manage to dismantle Hamas. NPR’s Tom Bowman, who covers the Pentagon, raised these issues, asking, “You destroy Hamas, but who governs Gaza? And are you creating more militants by your tactics?”
The US has an urgent responsibility to address these concerns and to restore respect for international law. It has acted since the end of the Cold War as somewhat above the law. Its failure to model law compliance and support an accurate reading of the UN Charter, the Geneva Conventions and other fundamental law has helped undermine respect for legal prohibitions on the use of force, the principle that underlies all others.
Biden has the opportunity to change the reality on the ground — for Israelis and for Palestinians — by using the power of the purse to win law compliance and the conditions for enduring peace. He can begin by winning an immediate ceasefire.