Foreign Policy Research Institute A Nation Must Think Before it Acts Conflict in Gaza: The Law of War and Irregular Warfare in Urban Terrain
Conflict in Gaza: The Law of War and Irregular Warfare in Urban Terrain

Conflict in Gaza: The Law of War and Irregular Warfare in Urban Terrain

  • Jim Petrila
  • March 5, 2024
  • Center for Intelligence and Nontraditional Warfare

Bottom Line

  • International Humanitarian Law, generally called the Law of Armed Conflict in the United States, applies to the current fighting in Gaza. These core principles are outlined in the Geneva Conventions of 1949 and Additional Protocols of 1977.

  • The four basic principles of International Humanitarian Law are distinction, military necessity, proportionality, and humanity. These principles acknowledge that civilian casualties will occur during armed conflict and seek to provide a legal framework under which armed forces will strive to limit such collateral damage to both people and property to the greatest extent possible.

  • While these principles are easily described, the implementation of International Humanitarian Law in practice involves difficult and controversial judgments that weigh military necessity against likely collateral damage, including civilian deaths. There is a built-in asymmetry when the conflict occurs in densely populated areas where one party to the conflict does not view itself as constrained by International Humanitarian Law.

  • Given the high level of support that the United States has provided and will continue to provide to Israel, it is in America’s national security interest to ensure that the Israel Defense Forces follows the principles of International Humanitarian Law.

Note from Philip Wasielewski, director of FPRI’s Center for the Study of Intelligence and Nontraditional Warfare:

The conflict in Gaza is a classic example of irregular warfare, a form of warfare in which one side fights another to achieve political goals via indirect methods such as insurgency, subversion, and terrorism and the methods used by the other side to defeat that effort. For the terrorist group Hamas, the tactic of hiding amongst civilians allows it to fight the much stronger state actor, Israel, on almost an equal footing. Israel’s political goal in Gaza, to destroy the force that massacred its citizens on October 7, is complicated by both Gaza’s urban terrain and Hamas’ tactics. Hamas has ensured via its tunnel system under civilian housing, use of protected sites (e.g., hospitals, mosques, etc.), and refusal to meet the standards of lawful combatants (e.g., wearing of uniforms, adhering to the Laws of Armed Conflict, openly carrying weapons), that any military action against them will result in substantial civilian casualties. While losing many fighters and civilians in the tactical fight, its tactics may cause Israel to lose the strategic contest by turning world opinion against it and ending a peace process between Israel and various Arab neighbors.

Although the United States faced a similar problem of irregular warfare in an urban environment in Iraq, particularly with its own soldiers fighting in Baghdad, Fallujah, Ramada, and in Mosul in an advisory capacity, it has yet to face the sheer scale of urban warfare that Israel does now. The entire campaign is being conducted in urbanized terrain twice the size of Washington D.C., containing over two million people.

This is not a unique problem nor one that will go away for Israel or the United States. According to UN data, over half of the world’s population is urbanized and there are now over eighty-one cities with populations of over five million people. Furthermore, many cities and mega-cities in low-income countries consist not only of a large built-up central area but are also surrounded by sprawling encampments or suburbs that can cover a hundred square miles or more.

Therefore, Israel’s dilemma in Gaza today may become America’s dilemma tomorrow. The United States should pay close attention to determine what its military might have to do in a similar situation and refine its doctrine, tactics, techniques, and training for irregular warfare in an urban environment. Most importantly, the United States should consider beforehand what its strategy might be to deal with the conundrum that terrorists force the government into when operating in dense urban terrain.

As a beginning of the process to develop that strategy, James Petrila, a national security lawyer with extensive experience at the National Security Council, Central Intelligence Agency, and National Security Agency, has written the article below discussing the legal requirements and ramifications of conducting military operations in an urban environment against a foe that does not follow the Geneva Conventions and purposely imbeds itself within the civilian population. Understanding these requirements for a society guided by the rule of law is the first step in developing a politico-military strategy to fight terrorist forces embedded in a major urban area. Petrila’s work not only describes those legal requirements for the layman, but hopefully will also guide the future policymaker. The four basic elements of International Humanitarian Lawdistinction, military necessity, proportionality, and humanity—that Petrila describes cannot be fully implemented unless the fighters on the ground have a strategy to guide them regarding a political end state, which will help them make decisions under the extreme stress of combat what is necessary, proportional, and humane.

As Clausewitz informs us, the trinity of war consists of primordial violence, chance, and reason. A proper strategy can provide armed forces with the reason and clarity to use violence for a political end and not for its own sake alone. Otherwise, a nation’s strategy to eventually end the war will be left to chance. The below article on the legal ramifications of fighting under such difficult circumstances can hopefully guide future discussions on this very complicated and emotional subject.

– Philip Wasielewski



Since Hamas’ brutal terrorist attack on Israel on October 7, the Israeli response in Gaza over the past several months has led to scrutiny on whether Israel has violated the core principles of International Humanitarian Law (IHL). These core principles of IHL (in the United States generally referred to as the Law of Armed Conflict, or LOAC) have developed over time and aim to govern the conduct of states and individuals during both international and non-international armed conflict. These principles of distinction, military necessity, proportionality, and humanity are easily summarized, but applying these principles under current conditions in Gaza is exceedingly difficult.

Israel has consistently asserted that its military actions in Gaza are consistent with IHL. As the number of civilian casualties continues to grow (currently estimated at 30,000 deaths and twice that number wounded), and the number of well-publicized incidents (e.g., the recent incident involving an aid convey in Gaza that resulted in the deaths of over a hundred people; attacks on the Maghazi refugee camp and the tragic killing of three shirtless hostages waving white flags) there are increasing public challenges to Israeli assertions, particularly regarding the principles of distinction and proportionality. The Israel Defense Forces (IDF), on the other hand, continues to produce evidence to support their claims that Hamas deliberately has put civilians at risk by using otherwise protected areas such as hospitals, mosques, and schools, for military purposes. The extent of Israeli compliance with IHL during its current military campaign against Hamas and Hamas’ violation of it by deliberately putting civilians at risk will most certainly enter the long list of charges and countercharges that have characterized the Israeli-Palestinian dispute since Israel was established in 1948. The purpose of this article is simply an attempt to provide a basic summary of the core principles of IHL, which are contained in the Geneva Conventions of 1949 and the Additional Protocols of 1977, and to point out some of the difficulties in applying these principles to the facts on the ground.

As an initial matter, there is no doubt that IHL applies to the current conflict between Israel and Hamas. Whether Hamas is viewed as a terrorist group, a non-state actor, or something else, the current fighting in Gaza can be characterized as a non-international armed conflict and IHL principles clearly apply. Israel’s military action against Hamas following the horror of October 7 clearly and legitimately is based on Israel’s right to self-defense. Given the high level of support that the United States has provided and will continue to provide to Israel, it is in America’s national security interest to ensure that the IDF follows the principles of IHL. Additionally, there is a high degree of asymmetry involved, since the military wing of Hamas is a terrorist organization that unapologetically and with impunity defies every aspect of IHL—not only in its horrific October 7 attack, but in its entire military strategy, which is based on hiding itself within Gaza’s civilian infrastructure. Israel, on the other hand, remains sufficiently committed to the core principles of IHL that, even in the midst of a brutal war, it investigates its actions, and admits to mistakes (e.g., recently admitting that its bombing of the Maghazi refugee camp caused “unintended harm to uninvolved citizens” as a result of using weapons that were unsuitable for the nature of the military action).

The Four Basic Principles of International Humanitarian Law


The principle of distinction, added to the Geneva Conventions by the 1977 Additional Protocols, requires parties to a conflict to distinguish at all times between the civilian population and combatants, civilian objects and military objects, and to direct operations only against military targets. An uncomfortable underpinning of IHL is that it contemplates that civilians will be killed in warfare. Distinction is the most humanitarian of the basic principles, in that it requires military forces at all times to distinguish between military and non-military personnel and military and non-military targets.

The IDF faces an immediate dilemma in that Hamas forces do not wear uniforms, but instead hide within the population of Gaza. Hamas’ military infrastructure also is deeply embedded within the civilian infrastructure of Gaza, making it difficult to make the distinction between military and civilian targets. In fact, the Gaza Ministry of Health, which is the primary source of information about casualties in Gaza, does not distinguish between civilian and militant deaths and injury.

The issue of identifying legitimate targets is not unique to the current situation in Gaza. The United States has faced this issue since the 9/11 attacks, both in terms of “unlawful combatants” detained at Guantanamo Bay, but particularly in the use of drone signature strikes against al-Qaeda, the Islamic State, and related terrorist targets in Afghanistan, Pakistan’s Federally Administered Tribal Areas, Yemen, and Syria.

Of perhaps greater relevance to the current fighting in Gaza, US armed forces faced these issues in close combat in Iraq. During the Second Battle of Fallujah, a city of approximately 250,000 persons, an estimated 800 civilians died, even when US forces were able to evacuate or encourage much of the civilian population to leave before combat operations began. During the fighting to retake Mosul, a city of over 1.5 million people, the Islamic State did not allow the population to flee, and consistently used the local population as human shields. The result was a much higher level of civilian casualties; most estimates of civilians killed are between 9,000 and 10,000, though the actual number likely will never be known because of the massive destruction of buildings and the likelihood that many people were buried in the rubble.

The Israeli Supreme Court confronted the issue of targeted killings by Israeli armed forces during the Second Intifada. In a decision handed down in 2006 in a case brought by the Public Committee Against Torture in Israel, the Israeli Supreme Court addressed the issue of whether preventive strikes against Hamas targets were legal. A critical issue before the court was whether terrorists involved in the Intifada were combatants, unlawful combatants, or civilians. In reviewing the current state of IHL, the court rejected the argument put forward by the Israeli government (as the defendant in the case) that there is a separate category of “illegal combatant.” The court instead held that there are only two categories: combatants and civilians. The court held that terrorists, to include those fighting for Hizballah and Hamas, are not combatants as defined by international law because they do not follow the laws and customs of war. As civilians, however, who take direct part in hostilities, they are not protected from being military targets. The court then provided a broad definition of what it means to take direct part in military activities, including such activities as collecting intelligence, transporting fighters to or from places where hostilities are taking place, operating or servicing weapons, or serving in a command position. Note that the Israeli supreme court’s definition largely mirrors the United States definition of material support to terrorism found at 18 USC Section 2339B, though the US definition of “material support includes financial support as well.”

This decision is important in that it provides the Israeli legal basis for military actions in Gaza, even though the current scale of military action far exceeds the targeted killings that were part of the Israeli defense against the widespread terrorist attacks that the Second Intifada directed against Israeli civilians and resembles more the level and type of combat in Fallujah and Mosul.

The principle of distinction covers not only people but also places. Certain areas, including hospitals, are presumed to be civilian in nature and protected from military attack. Protected sites lose their protected status, however, if they are used for military purposes. In such cases, the burden is on the side conducting the attack to make the case that the site has lost its protected status. To be consistent with IHL, this determination must be made based on information available before the attack.

The Israeli government has claimed that the military’s decision to engage in action against the al-Shifa Hospital in Gaza City was based on credible and convincing intelligence information that Hamas was using the hospital for military purposes. While the Israelis have released some information justifying their attack, they have not released their full justification, since it appears that at least a portion of their justification relied on sensitive intelligence sources or methods of collection. The United States recently declassified a limited amount of intelligence, concluding that the al-Shifa Hospital had in fact been used operationally by Hamas. Several Western press reports, including by the Washington Post, have assessed that the information publicly released to date by Israel has not made that case.

To ensure consistency with the Israeli legal interpretation of IHL, planned targets of the Israeli military campaign must be assessed under the principle of distinction, which is a significant challenge in a fast-paced and relentless bombing campaign in a dense urban environment against an enemy whose tactics are based on hiding among the civilian population. The current campaign potentially has raised new issues. For instance, news reporting has indicated that the IDF has been relying on artificial intelligence programs to assist in military targeting. It is unclear how artificial intelligence programs are being used and whether artificial intelligence assists, or has replaced, human decision-making in the targeting process. If the news reports are accurate, the IDF may be breaking new ground in terms of how its use of artificial intelligence fits into the concept of distinction.

Military Necessity

Military necessity allows all measures necessary to accomplish a legitimate military purpose so long as these measures are not otherwise prohibited by IHL. It is a legitimate military purpose to defeat the enemy as quickly and efficiently as possible, but military necessity does not allow disproportionate or indiscriminate targeting, nor does it allow activities whose purpose is to spread terror among a civilian population. As stated in Article 54 of the Additional Protocol, an attacking force is not permitted to destroy “objects indispensable to the survival of the civilian population.” Within the framework of military necessity, the IDF has imposed a significant blockade of Gaza, has limited relief supplies and has periodically cut electricity and communications within Gaza. The dilemma faced by the IDF is that efforts to degrade Hamas’ fighting capability also render hardship to the civilian population. The longer the armed conflict goes on, the greater the harm to the civilian population, and the greater the likelihood that Israel will face increased international pressure to shift its military tactics to ease the hardship so far imposed on the civilian population of Gaza.


Proportionality recognizes that incidental harm will occur to civilians during military operations. It should be noted that the focus of IHL is on limiting the inevitable civilian deaths that occur in military action. A detached discussion of the principles and the unfortunate realities of war does not in any way lessen the suffering and sense of loss that occurs with each civilian death or injury. As with the principle of distinction, proportionality as a concept asks the question of whether anticipated harm to the civilian population is “excessive” relative to the military advantage that is anticipated from the military action.

In general, proportionality requires judging each attack on its own merits. In a campaign as massive as Israel’s current military efforts, proportionality judgments must be made countless times each day, and each command decision ultimately is a judgment call that is linked to specific rules of engagement. Because proportionality assumes collateral damage, both to civilians and to property, an objective assessment becomes very difficult. The trade off in a decision to bomb in an urban environment—projected military advantage versus anticipated civilian death and injury—inherently leads to decisions that will be controversial.

At the tactical street level in an urban environment, snap judgments must be made, often with tragic consequences, as in the case of the three hostages who were killed by Israeli troops. The IDF has taken steps to attempt to limit civilian damage, such as issuing evacuation orders before launching military strikes. In the midst of the current military campaign, it is difficult to assess the effectiveness of these steps. The concept of proportionality is particularly difficult in the current situation in which the majority of the population of Gaza has been largely displaced. As the military action continues and intensifies, it is reasonable to assume that the number of civilian deaths, already estimated at 30,000, will continue to mount.


The fourth IHL principle is humanity, found in Article 35, which has two major provisions. The first prohibits the use of weapons intended to cause “superfluous injury or unnecessary suffering.” The second prohibits employing methods intended or likely to cause widespread and long-term severe damage to the natural environment.

Moving Forward

Israel’s military action in Gaza is an understandable reaction to the horrific Hamas actions of October 7, but the length and extent of the military action also will shape the reactions of Palestinians for the foreseeable future. Both October 7 and the Israeli response will enter the realm of historical memory. The periodic fighting between Israel and Hamas, particularly since Hamas gained control of Gaza in 2007, should not inspire confidence in anyone that a lasting peace is a likely outcome. An adherence to IHL, however, is a necessary component to enhance the chances of a longer lasting political settlement once the current military campaign ends.

It also is clear that the necessity of adhering to IHL is one that should apply to all parties in the conflict. If the collective and extensive experience in counterterrorism operations since the 9/11 attacks has demonstrated anything, it is that terrorist organizations such as Hamas will continue to ignore IHL with impunity. This creates an obvious asymmetry in the conduct of the war, but it is a reality with which the IDF must live.

There has been reporting that the Biden administration has insisted that Israel begin to think about possible political solutions for “the day after.” For years, Gaza has been a small strip of land inhabited by some two million people, most of whom are legally stateless. The view of the Biden administration seems to be that this situation is not sustainable in the long term, particularly after so much of the civilian infrastructure within Gaza has been damaged or destroyed.

This view, however, does not appear to be shared by the Israeli government. In a recent op-ed, Prime Minister Benjamin Netanyahu listed three goals that his government hoped to achieve through military action. They include the destruction of Hamas, the demilitarization of Gaza, and the deradicalization of Palestinian society. Recent reporting on current tensions between the United States and Israel has focused on the differences in what “the day after” might look like in Gaza. These differing views can be reflected in military tactics and the amount of collateral damage that is viewed as consistent with IHL.

Absent the complete obliteration of Gaza, it is unlikely that Hamas, an organization that is politically and militarily enmeshed within Gaza society, will be totally destroyed. Israeli military action certainly can significantly degrade Hamas’s capabilities and military necessity can justify actions to destroy Hamas’s military infrastructure, including its massive network of tunnels. But is the total destruction of Hamas militarily and politically an achievable goal? The demilitarization of Gaza is a goal well worth achieving, but absent a meaningful political solution that does not involve Israeli occupation of Gaza, is that an achievable goal in either the short or long term? Finally, it is difficult to see the path to the deradicalization of Palestinian society under the current circumstances.

On the other side of the ledger, how much of the current Israeli strategy is intended to cause sufficient pain and suffering to the people of Gaza so they turn on Hamas as the cause of the military conflict? Intentional infliction of damage on civilian populations is inconsistent with the principle of distinction, since civilian populations not directly engaged in hostilities by definition are not legitimate targets. Does the Netanyahu government believe that the only way to “deradicalize” Palestinian society is through the current tactics being deployed in Gaza? In either case, adherence to IHL requires serious efforts to continue to distinguish between military and non-military targets and to ensure that military necessity and proportionality judgments continue to be made so long as this conflict continues.

The Israeli government has been consistent in stating that it is prepared for a long war in Gaza. Since Israel’s stated goals will be extremely difficult to achieve in the short term, the logical conclusion is that the war will continue for an extended period of time. As the IDF tries to root out Hamas strongholds in an increasingly degraded urban landscape, it will become increasingly difficult to adhere to the requirements of distinction and proportionality. As capable and well-trained as Israeli forces are, urban warfare against a determined enemy for whom IHL is meaningless will continue to be an exceedingly difficult task, but one to which the IDF nonetheless must remain committed.

The views expressed in this article are those of the author alone and do not necessarily reflect the position of the Foreign Policy Research Institute, a non-partisan organization that seeks to publish well-argued, policy-oriented articles on American foreign policy and national security priorities.

Image: (Photo by Majdi Fathi/NurPhoto via Reuters)