Israel has been at war against Hamas in Gaza for almost half a year; Russia attacked Ukraine two years ago. At the beginning of both conflicts, the precipitating cause for war was self-defense—against terrorist violence from Hamas and against Russia’s commitment to topple Ukraine’s pro-Western democratic government. Both Israel and Ukraine were victims of attacks on their own soil, leading them into conflicts that by almost any definition would be called just. But as these wars persist, it becomes increasingly difficult to answer the question of how further violence can be compatible with an ultimate path to peace.
In Gaza, even though there may be glimmers of hope for a pause in the conflict, there is no movement toward a lasting settlement. At press time, Hamas’s leadership was reported to be still deliberating a proposal for an extended cease-fire in exchange for hostage releases. One of the sticking points is that rather than seeking a permanent truce, Israeli leadership has remained committed to continuing its military operation, which has resulted in the deaths of more than 27,000 Gazans out of a population of 2.3 million, 85 percent of whom have been driven from their homes. The Israeli government, led by Prime Minister Benjamin Netanyahu, remains steadfast not only in insisting that Hamas cannot remain in power in Gaza, but also in rejecting any future possibility of a Palestinian state. At the same time, the risk of a wider regional conflict grows as the United States retaliates against Iranian-backed militias for a drone attack in nearby Jordan that killed three U.S. service members.
These endless engagements seem to continue because leaders simply cannot find any way out other than defeat.
In Ukraine, the war appears to be growing even more entrenched. Ukraine’s initial success in pushing Russia’s invasion back largely stalled in 2023, with the frontlines remaining stable for most of that time. There are no publicly acknowledged negotiations for an end to hostilities, but Ukraine’s ability to continue resisting Russia is threatened by the uncertainty of U.S. funding, which has been mired in partisan divisions over U.S. border policy. Ukraine’s stated aim remains the expulsion of Russia from both its eastern provinces invaded in 2022 and from Crimea, which Russia illegally annexed in 2014.
“There is no such thing as a just war: They do not exist!” Pope Francis spoke these words in March 2022, lamenting the Russian invasion of Ukraine. And indeed, the savagery of war in the 21st century can bring the most idealistic world leaders and politicians to a certain realpolitik, or even defeatism, over the possibility of conducting a military campaign according to the principles of just war theory.
Even wars that begin for the most just reasons imaginable can grind on and become “forever wars.” These endless engagements seem to continue because leaders simply cannot find any way out other than defeat. This is a lesson the United States has been taught, even if it has not fully learned it, in Vietnam, Iraq and Afghanistan. Rumors that Pope Francis might formally abandon just war theory have not been borne out, but his cri de coeur against the injustice of war and his calls for peace have been consistent. While many have critiqued his commitment to peace as naïve in the face of the threats posed by aggressors, Francis has continued to denounce violence in Ukraine and Gaza.
It is understandable, especially in the aftermath of an assault by an armed aggressor, to focus on self-defense as a just cause for war. However, just war theory, first laid out by St. Augustine in the fourth century, always involves other concerns as well, including conditions on how war is conducted—such as the proportionate use of force and the avoidance of harm to noncombatants. But the overriding concern is that the goal of a just war must always be to restore or establish peace.
A later criterion added to the just war theory, elaborated in the 16th century, sharpens the question of how the violence of war can be aimed ultimately at peace. It asks whether the use of force has a reasonable chance of success. And those asking the question must remember that “success” is not defined solely in terms of tactical and strategic objectives but necessarily includes the just goal of establishing peace.
The point of just war theory is not to make it easier to legitimize wars for a just cause, but to limit the ways the violence of war can be justified.
Judging what constitutes a “reasonable chance,” of course, is subject to extensive disagreement in practice. But such disagreement should not become a license to justify violence until those calling for peace can provide an alternate means to achieve it. War must be a last resort and once joined, wars must have an end, both in the sense of an ultimate goal of peace and in the sense of being able to finally conclude. They cannot be allowed to continue simply because they have begun.
U.S. support for both Ukraine and Israel began in understandable recognition of the justice of their causes. But as these wars continue, the United States has a responsibility to challenge our allies to explain how they are expected to end. In Europe, that means a realistic assessment of whether Ukraine can regain its full territorial integrity or whether the current frontlines of the war should be understood as an acceptable ceasefire line to be held to deter further Russian aggression until a negotiated peace comes into view.
And in Gaza, it means that the United States cannot ignore the Israeli government’s ongoing rejection of a two-state solution, which the international community has supported as the path to peace. That does not mean that Israel has to follow international dictates—but it should mean that Israel has to explain how it intends to establish a just peace that respects the rights and dignity of Palestinians in the territories it occupies or controls. It is the lack of any credible answer to that question, in addition to the disproportionate destruction of civilian life in Gaza, that motivates opposition to Israel’s use of force. Crucially, without that answer, Israel’s military efforts cannot succeed in making it safe in the long term, but only in returning to the status quo ante of Palestinian resentment of and resistance to Israeli rule.
The point of just war theory is not to make it easier to legitimize wars for a just cause, but to limit the ways the violence of war can be justified. If its hardest questions cannot be answered well, then even those who support a just cause have a duty to reject violence rather than pretending it aims at a peace it can never deliver.
