Source CSIS

WASHINGTON, US: Israel and Lebanese Hezbollah continue to escalate in what Israel has called Operation Northern Arrows.1 In mid-September 2024, Israeli intelligence sabotaged thousands of Hezbollah beepers and walkie-talkies, detonating them in an operation that killed dozens of group members and wounded thousands more. On September 27, 2024, Israel killed Hezbollah’s leader Hassan Nasrallah in an airstrike on the group’s Beirut headquarters—the culmination of a campaign against Hezbollah’s leaders that led to the killing of numerous senior group leaders in September 2024. 

 Two days before the Nasrallah assassination, Lieutenant General Herzi Halevi, chief of the general staff of the Israel Defense Forces (IDF), told Israeli troops from the Seventh Brigade deployed along the northern border, “We are preparing the process of a manoeuvre, which means your military boots . . . will enter enemy territory.”2 The IDF also called up two reserve brigades for what it referred to as “operational missions in the northern arena.”3 Israeli commandoes have conducted cross-border operations to gather intelligence and otherwise prepare for a ground invasion, and Israel has done limited operations so far in southern Lebanon.4 Iran responded by launching waves of ballistic missiles and other stand-off weapons at Israel.

 To better understand the prospect of further escalation, this brief asks four questions: What are Israel’s and Hezbollah’s objectives? How has violence evolved over the past several months? What are plausible scenarios for further escalation? What options do the United States and other countries have to mitigate or prevent escalation? To answer these questions, this analysis draws on a mixture of quantitative and qualitative information. It compiles data on Israeli and Hezbollah strikes along the Israel-Lebanon-Syria border and geolocates Hezbollah attacks against Israel in the demilitarized zone between the Blue Line and Litani River.

 The data show the increased scope and scale of Israeli and Hezbollah operations in recent months. Although most strikes by both sides have been within a relatively narrow area along the Israel-Lebanon border, the nature of the limited war between Hezbollah, Iran, and Israel is rapidly changing. Israel has escalated the number of strikes and the depth of its targeting. Hezbollah too has increased strikes, though in a far more limited way than Israel. And Iran has become directly involved in the conflict by firing ballistic missiles at Israel.

 Despite the growing risk, an all-out war is not inevitable. Israeli attacks might successfully coerce Hezbollah to accept a ceasefire and move forces away from the border, or they might significantly weaken Hezbollah’s capabilities to strike Israel. But if negotiations fail to establish a buffer zone along the Israel-Lebanon border, there is a heightened possibility of all-out war. Escalation could lead to significant casualties for both Hezbollah and the Israeli military, put Israeli civilians throughout the country at risk, lead to hundreds and perhaps thousands of Lebanese civilian casualties, and spread to Iran, Syria, Iraq, Yemen, and other countries.

 To explore the implications of escalation, the rest of this brief is divided into four sections. The first examines likely Israeli and Hezbollah objectives. The second assesses the evolution of violence. The third explores plausible scenarios of further escalation, and the fourth explores U.S. policy options.

 Strategic Objectives

 Shortly after the 1979 Iranian revolution, Iran’s Islamic Revolutionary Guard Corps (IRGC) helped establish Lebanese Hezbollah and provided money, equipment, training, and strategic guidance to the fledgling Shia organization.5 In addition, Iran sent as many as 1,500 IRGC advisers to the Bekaa Valley in Lebanon to build and run training camps that prepared Hezbollah fighters for war with Israel.6 Hezbollah played a major role in Israel’s 1985 decision to withdraw to a buffer zone on the Lebanese border and its 2000 decision to withdraw from Lebanon completely. Hezbollah, since its establishment, has defined itself in opposition to Israel. Its main objectives have been to drive Israel out of Lebanon and, ultimately, to destroy the state of Israel. In the 1980s and 1990s, Israel and Hezbollah regularly attacked each other despite the presence of the United Nations Interim Force in Lebanon (UNIFIL) along the Israel-Lebanon border, which is typically known as the Blue Line.

 After Israel withdrew in 2000, Hezbollah continued occasional attacks on Israel and conducted a series of attacks against Israeli interests and citizens across the globe. This limited conflict flared into an all-out war in 2006 after a Hezbollah cross-border kidnapping operation. The war left over 100 Israelis and around 500 Hezbollah fighters dead and devastated Lebanon. The 2006 war ended with United Nations Security Council Resolution (UNSCR) 1701. Among other measures, UNSCR 1701 created a demilitarized zone between the Blue Line and Litani River along the borders of Israel, Lebanon, and Syria (Figure 1). Weapons and fighters that did not belong to the Lebanese government or the United Nations (i.e., those of Hezbollah) could not pass south of the Litani River.

 After 2006, an uneasy status quo prevailed. Israel occasionally attacked Hezbollah fighters, and Iranian arms shipments headed to Hezbollah and other groups in Syria. There were intermittent rockets and drones and other standoff attacks across the border. For the most part, however, the border was the calmest it had been in decades.8 Another area of dispute was the village of Ghajar, just west of Shebaa Farms and bisected by the Israel-Lebanon border. Its residents have both Lebanese and Israeli citizenship.9 For years, a fence divided Ghajar, but in 2006 Israeli forces reoccupied the entire village and today retain control.

 Over the past year, however, several factors have changed the dynamics between Israel, Hezbollah, and Iran. First, the October 7, 2023, Hamas attacks in Israel dramatically increased Israeli insecurity and took a psychological toll on Israelis.10 Israel’s risk tolerance significantly changed. If Hamas could kill over 1,100 Israelis in a surprise cross-border operation, what could a much better organized, armed, and trained Hezbollah do? Hezbollah’s close relationship with Iran and ties to Hamas reinforced this fear. Second, the repercussions of the October 7 attack and clashes between Hezbollah and Israel displaced more than 150,000 people on both sides of the Israel-Lebanon border after October 2023, including over 62,000 civilians from northern Israel and more than 92,000 from southern Lebanon.11 The continuing displacement has put pressure on Israeli leaders to contain the Hezbollah threat to northern Israel so that residents can return.12 Third, Hezbollah has dramatically improved its military and stockpiled more than 150,000 standoff weapons in Lebanon and Syria.13 With Iranian partner and proxy forces active in Lebanon, Syria, Iraq, and other countries across the region, the threat from the north could get worse over time, not better.

 Based on these changes, Israeli leaders likely have several main objectives. The first is to curb the Hezbollah threat to Israel by seriously degrading Hezbollah’s military capacity and deterring further actions against Israel. As Israeli defense minister Yoav Gallant remarked, a key Israeli goal is “destroying Hezbollah’s capabilities that have been built up over 20 years,” including “disarming entire units of the Radwan force and leaving Nasrallah alone at the top of Hezbollah.”14 As the Nasrallah killing, beeper operation, large-scale air attacks, and ground operations showed, Israel is increasingly shifting from a traditional deterrent approach of threatening punishment to one of weakening Hezbollah’s capabilities to the point that the group cannot effectively respond.

 Hezbollah has repeatedly fired anti-tank guided munitions (ATGMs), rockets, drones, missiles, and other standoff weapons at Israeli military and civilian targets from south of the Litani River and other locations in Lebanon. Figure 2 displays possible launch areas for Hezbollah ATGM attacks based on geolocated footage of ATGM impacts shown in Hezbollah propaganda videos.15 These attacks are a clear violation of UNSCR 1701. Hezbollah’s elite Radwan forces have also been deployed along the border. Thanks to Iranian assistance, Hezbollah possesses as many as 200,000 standoff weapons, including short- and long-range unguided rockets, short- and intermediate-range unguided ballistic missiles, and short- and medium-range guided ballistic missiles such as the Fateh-110/M-600 and Qadr-1.

 A second Israeli objective is to resettle Israel’s internally displaced population back to their homes and villages in northern Israel. Doing this requires establishing and sustaining a security environment that currently does not exist. Prime Minister Benjamin Netanyahu stated it would be impossible to return Israeli civilians to their homes without a “fundamental change in the security situation in the north,” an attitude that appears to be driving Israel’s recent escalation.16 Defense Minister Gallant added, “We will continue with additional blows that are already prepared until we achieve our goal—the return of the residents of the north to their homes, to achieve the goal we are willing to take any action.”17

 Escalating Violence

 The escalation of violence in late September far surpasses any other phase of the Israel-Hezbollah conflict. After conducting an average of about 160 attacks each week for the 11 months following October 7, Israel struck Lebanon more than 300 times in the week of September 15 and more than 700 times in the week of September 22.

 But even before Israel commenced Operation Northern Arrows in September, there were indications the conflict was entering a new phase. The number of violent incidents related to the Israel-Hezbollah conflict fluctuated between 150 and 250 incidents each week between October 7, 2023, and August 18, 2024. But late August saw the number of incidents rise past 280 per week, with Israeli attacks driving most of the increase. Another sign was an increase in Israeli warplanes conducting threatening overflights over Lebanon (Figure 4). Before summer 2024, these incidents were extremely rare, but Israel sent warplanes over Lebanese cities with increasing frequency throughout the summer, frequently breaking the sound barrier in what now seems to be an implicit threat.

 During the summer, most of the violence took place in the vicinity of the Blue Line (Figure 5). Hezbollah and Israel have traded artillery, ATGM, and air and drone strikes across the border almost daily since October. Before the beginning of Operation Northern Arrows, the fighting displaced roughly 60,000 Israelis and 110,000 Lebanese.19 The fighting has resulted in a major increase in displacement and death since the beginning of Operation Northern Arrows, with Lebanese authorities reporting that more than 90,000 people were displaced and 600 were killed between September 24 and September 26.

 The violence has not remained limited to southern Lebanon or northern Israel; it has expanded deeper into both countries. Israel has conducted long-range strikes into Lebanon since early 2024, and both the frequency and depth of these strikes have increased over time (Figure 6). Between October 7, 2023, and August 31, 2024, the average Israeli strike occurred about 4 km into Lebanon. In the first three weeks of September, the average depth of an Israeli strike was approximately 6 km. During the week of September 22, the average depth of an Israeli strike was 27 km.

 The highest-profile deep strikes have been the assassinations of Hezbollah leaders in Beirut, but the IDF has also repeatedly attacked Hezbollah’s logistics and air defense infrastructures. The IDF does not appear to be limiting its deep strikes to symbolically or politically important targets but seems to have been engaged in a campaign to degrade Hezbollah’s ability to supply and protect its forces throughout Lebanon.

 Despite promises by Hezbollah and Iranian leaders to escalate in response to Israeli deep strikes, Hezbollah’s success has been mixed.21 As shown in Figure 7, Hezbollah attacks have reached deep into Israel on far fewer occasions than Israel has struck deep into Lebanon. This may be, in part, due to the efficacy of Israeli air defenses like Iron Dome and David’s Sling, but Hezbollah restraint and Israeli deterrence have played a role. For more than a decade, Hezbollah has possessed standoff weapons capable of striking all of Israel, but it has not appeared to use them in response to any of Israel’s deep strikes, generally retaliating with an increase in short-range rocket or ATGM fire into northern Israel.22 Hezbollah has also kept its rocket attacks small relative to its total launch capacity, which is frequently estimated to be more than 1,500 rockets per day.

 Hezbollah has, however, managed to escalate the depth of its attacks, if not their number. As shown in Figure 8, the average depth of Israeli and Hezbollah attacks has moved roughly in parallel since October 7. Between October 7, 2023, and August 18, 2024, the average Hezbollah strike occurred about 3 km into Israel. Between August 18 and the beginning of September, the average depth of a Hezbollah strike was approximately 4 km. During the week of September 22, the average depth of a Hezbollah strike was 28 km. Hezbollah has conducted far fewer attacks than Israel since the beginning of Operation Northern Arrows, probably due to the pressure created by Israel’s recent killings of Hezbollah leadership, penetration of the group’s communications, and bombing of rocket and missile systems.

 Hezbollah has recently escalated its long-range attacks with a September 25 missile attack that apparently targeted the headquarters of Mossad, Israel’s main external intelligence agency, near Tel Aviv. Although Israeli air defense systems intercepted the attack, Hezbollah signaled that it is willing target Israel’s largest city.24 But the attack has not yet developed into a campaign of long-range strikes against Israel, possibly because of the amount of pressure from Israel’s recent killings of Hezbollah leadership, penetration of the group’s communications systems, and bombing of rocket and missile systems.

 The conflict underwent a further escalation on October 1, when Iran launched about 180 ballistic missiles at Israel.25 The attack marked only the second direct attack on Israel launched from Iranian territory. Israel’s response remains uncertain; it responded to Iran’s previous missile attack with an implicit threat to destroy Iranian nuclear infrastructure.26 The region is currently teetering on the brink of all-out war. More direct attacks between Israel and Iran will probably push it over the edge.

 Scenarios for Escalation

 In light of the escalating violence, this section examines three scenarios for further escalation: an Israeli ground invasion, a coercive Israeli air war, and a major Hezbollah escalation.

 Ground Invasion

 Israel might conduct a major and sustained ground incursion into southern Lebanon to drive Hezbollah forces away from the Israel-Lebanon border, ideally up to or past the Litani River. In essence, the goal would be to recreate something like the buffer zone Israel held from 1985 to 2000, when the cumulative weight of Hezbollah attacks led Israel to withdraw. The operation might require large numbers of Israeli ground forces (in 2006 Israel sent around 30,000 troops into Lebanon—a number that was probably insufficient), both to suppress retaliatory Hezbollah missile and rocket fire against Israel and to support ground operations.27 Because Israeli forces have been fighting in Gaza or have been called up in other theaters for almost a year, reservists need little retraining.

 If successful, such an operation would greatly reduce the risk of an October 7–like ground incursion from Lebanon. Hezbollah fighters would need to traverse the buffer zone before crossing the Israeli border, making their detection and disruption far more likely. In addition, depending on the length of the buffer zone, Israel would reduce the risk of Hezbollah strikes from short-range systems such as mortars and especially ATGMs, making it hard for the group to fire into Israel proper. This, in turn, would make it safer for Israelis to return to their homes in northern Israel. Hezbollah would probably lose hundreds of fighters in the operation, perhaps even thousands—another blow to the group, which has suffered for months from Israeli strikes and covert operations against its personnel.

 The short- and long-term costs of such an operation would be significant. Almost a year of fighting in Gaza has strained the Israeli military, which relies heavily on reserves. Another major operation would place a high burden on Israeli society. Because of the skill of Hezbollah fighters and the years they have had to build tunnels and establish defensive positions, operations may need to move slowly or risk surprise attacks that could lead to significant Israeli casualties or the risk of Hezbollah taking military captives.28 Even with a cautious approach, Hezbollah likely would impose significant casualties on Israeli forces, as it did in 2006. In addition, a ground invasion could trigger a far more massive Hezbollah rocket and missile attack deeper into Israel, with large numbers of systems launched to overwhelm Israel’s air defenses.29 These systems could target the whole country and, because Hezbollah has some precision systems, pose a risk to important military and civilian sites.30 In the 2006 conflict, Hezbollah sustained rocket and missile attacks on Israel for all 34 days of the conflict.31 Israel’s recent operations against the group, however, may have degraded its ability (and thus its willingness) to engage in a massive response.

 The damage to Lebanon would be far more severe, with Israeli forces targeting Hezbollah infrastructure and fighters throughout the country. If the Gaza campaign is any guide, Israel would be willing to inflict significant damage to civilian infrastructure and kill many civilians in pursuit of military objectives. Hundreds of thousands of Lebanese might be displaced as well.

 Another vexing issue for Israel is the long-term status of the territory. Before 2000, Hezbollah regularly attacked Israeli forces and their Lebanese allies in the buffer zone, imposing low-level but steady casualties on Israel. Israeli forces were caught in the “Botz HaLevanoni” (the Lebanese muck) for 18 years. Given Israel’s 2000 abandonment of its Lebanese allies, it will struggle to find local allies to maintain the security zone, increasing both the risk of casualties to Israel and the number of troops needed to maintain the buffer zone. Iran would also help Hezbollah rearm and otherwise support the group as it recovers from Israeli attacks. With Israel occupying Lebanese territory, backing for Hezbollah is likely to increase, as Hezbollah can more credibly claim its operations are defensive and seek to restore the country’s sovereignty.

 Because of these risks, Israel might use a ground invasion supported by an aggressive air campaign to significantly degrade Hezbollah’s capabilities, destroy infrastructure (including tunnels) in the south, withdraw troops to Israel, and threaten to escalate if Hezbollah continues attacking. Economist and military strategist Thomas Schelling writes, “It is the threat of damage, or of more damage to come, that can make someone yield or comply.”32

 Coercive Air War

 Instead of a major ground invasion, Israel might conduct a sustained large-scale air campaign against Hezbollah and perhaps Iran and Iranian-backed groups.33 In such a scenario, piloted aircraft and drones would attack Hezbollah and other rocket and missile sites, ammunition stockpiles, command-and-control centers, and leadership targets, as well as interdict Iranian arms shipments to Hezbollah. In contrast to current operations, far more attacks would occur outside the border zone, especially in Shiite-populated parts of Beirut and the Bekaa Valley, both of which are long-standing Hezbollah strongholds. Such an operation would put far fewer Israeli personnel at risk and otherwise avoid many of the costs to Israel of a ground operation. The operation would have to be sustained for many days. For example, Operation Allied Force, the U.S. air operation that forced Serbia to make concessions on Kosovo, lasted 78 days.

 If successful, such an operation would continue to inflict a high pace of leadership turnover against Hezbollah.34 As a result, Hezbollah would continue to be off-balance and face difficulty drawing on the full strength of the organization. Attacks on Hezbollah’s military infrastructure would reduce the number of rockets and missiles Israel might face and make it harder for the group to deploy longer-range (and thus larger) systems without risk of detection and destruction.

 Although such an operation would be less destructive to Hezbollah than an Israeli ground operation, the constant killings and destruction might make the group more willing to accept a ceasefire independent of the outcome of the Gaza war. Hezbollah leaders might also fear that ordinary Lebanese would turn against them, blaming the group for Israel’s campaign of destruction.

 Hezbollah, of course, might not cave in the face of Israeli pressure. In the past, the group has proved willing to suffer considerable costs, including the loss of its most senior leaders, without abandoning its fight against Israel. Hezbollah may fear the public embarrassment of surrender, especially if Hamas and other Palestinian groups keep fighting. They may also believe they are in a use-or-lose situation with regard to some weapons systems. Moreover, by not using ground troops, Israel would be less effective at rooting out Hezbollah fighters near the border, who might hide underground or among civilians. In addition, the group’s short-range systems are less vulnerable to airpower. Hezbollah will also believe, probably rightly, that Iran will eventually replace many of the weapons systems Hezbollah would lose to air strikes.

 In any event, Lebanese civilians would suffer considerably from this operation. The Israeli military claims that many Hezbollah facilities are located near civilian sites and that the group has deliberately put weapons in civilian areas.35 Several conflicts between Israel and Hezbollah have ended, in part, because of high-profile Israeli attacks that mistakenly killed civilians. However, Israel’s approach to Gaza suggests international condemnations due to civilian deaths matter less in its leaders’ calculations than other factors. This campaign may also take weeks or even months to resolve, far longer than a ground operation.

 Hezbollah Counter-Escalation

 Hezbollah and Iran may decide to dramatically escalate operations against Israel. Israel’s recent attacks may lead group leaders to feel that their credibility is at stake if they do not respond. Hezbollah might also feel that Israel’s operations will be unrelenting, even if it does not retaliate, and thus the group may lose capabilities if it does not use them. A Hezbollah and broader Iranian decision to move to all-out war could involve a massive and sustained rocket, missile, and drone assault on Israel as well as limited ground operations on Israeli territory, though such ground operations are unlikely.

 A ground operation would be difficult under the present circumstances. Israel’s leadership attacks and the explosion of Hezbollah pagers and walkie-talkies have made command and control more difficult and thus make it harder for Hezbollah to coordinate a successful ground operation. In addition, Israeli forces on the border are reinforced and prepared for an attack. There would be little chance of surprise, and given the recent successes of Israeli intelligence, Israel may know about the attack well in advance and prepare a devastating response.

More dangerous for Israel is Hezbollah’s rocket, missile, and drone arsenal. Although Israeli air strikes have degraded some of this arsenal, Hezbollah still has much of it left, including large numbers of unguided missiles as well as smaller numbers of guided missiles that have the range to strike all of Israel. Hezbollah’s command-and-control systems also may be in chaos due to the various Israeli attacks. If Hezbollah could simultaneously launch large numbers of rockets and missiles, Israeli air defenses would down many, but Hezbollah could probably overwhelm Israeli defenses with massive simultaneous strikes and drone swarms.36

 Hezbollah’s goals would be as much political as military. If Hezbollah could conduct credible operations against Israel, it would offset some of the damage done to its reputation by Israel’s various intelligence successes. In addition, by inflicting steady punishment on Israelis throughout the country, Hezbollah would try to repeat its 2006 war success, when it created a sense among Israelis that they were involved in an unwinnable war.

 The risks for Hezbollah would be considerable. In addition to losing many of its fighters in ground attacks, the group might have an uncoordinated response and inflict only limited damage upon Israel, a further humiliation. Lebanon would suffer considerably from the Israeli response, and many Lebanese would blame Hezbollah, as well as Israel, for the destruction.

 Hezbollah may count on help from Iran, though Iran’s anemic response to Israeli attacks so far, its weak conventional military, and its distance from the theater make it a limited partner. Nevertheless, Iran would likely replenish Hezbollah’s matériel losses and provide financial support to help the group recover, as it did in 2006. Iran has also increasingly signaled its willingness to directly attack Israel in response to the Israeli threat to Hezbollah, and the Israeli response to Iran’s October 1 ballistic missile attack will risk further escalation between the two regional powers.

 Options for Mitigating a War

 The United States has engaged in near-constant diplomacy to bring about a ceasefire between Israel and Hezbollah since the crisis began. Although U.S. efforts have clearly failed, the United States did help convince Israel not to launch a preemptive strike on Hezbollah in the days after the October attack. Moreover, the United States has probably helped deter Iran from increasing its direct role and may be a factor in Hezbollah’s decision, so far, not to escalate to all-out war.37

 Amos Hochstein is the face of U.S. diplomacy in the Lebanon crisis, often working with French, and at times German, officials.38 He has put forward a plan to relocate Hezbollah forces north of the Blue Line and end Israeli overflights of Lebanon, which violate UNSCR 1701. Hochstein has advocated for additional observers (potentially from Germany) to the 13,000 UNIFIL troops deployed in southern Lebanon to better monitor potential Hezbollah activity there.39 Hezbollah, however, claims it will not end its attacks as long as Hamas is fighting, a stance it reiterated after the Nasrallah killing. Israeli officials claim diplomacy alone will not bring a ceasefire, and they call for Hezbollah to abide by UNSCR 1701, which prohibits the group from placing fighters near the Israeli border.

 Even as the United States has pushed for a diplomatic settlement, however, it has supported Israel militarily with equipment, ammunition, air defense, and intelligence, and it could continue to do so as a way to increase pressure on Hezbollah.40 Given the risk of all-out war, however, U.S. officials should redouble efforts to bring about a ceasefire in Lebanon, even if they cannot achieve one in Gaza. Hezbollah, given its recent losses, may be open to a ceasefire if it can occur in a face-saving way, which in practice may mean after Hezbollah successfully conducts a significant attack on Israel.

 As an alternative, experts like Middle East analyst Robert Satloff contend the United States might push for an informal deal where both sides suspend or significantly curb cross-border fire and civilians return to their homes. Under this proposal, Hezbollah would remove its major military systems from the area near the Israeli border. An Israeli concession would allow Hezbollah’s forces to return to the border but not in uniform or as part of large formations.

 Despite these diplomatic initiatives, a lasting ceasefire will be difficult to achieve. The October 7 Hamas attack was a landmark moment for Israel’s government and population, exacerbating the country’s insecurity. The best that negotiators may be able to achieve is managing the escalation of violence and preventing an all-out war that devastates much of Lebanon and expands into Syria, Iraq, Yemen, and other countries.