Escalating to War between Israel, Hezbollah, and Iran

The Issue

There is a serious risk of all-out war between Israel, Hezbollah, and Iran. According to new CSIS analysis, both the scale and geographic scope of violence have dramatically increased. The number of violent incidents related to the Israel-Hezbollah conflict increased 4.5 times in the last week of September from the weekly average between October 7, 2023, and August 31, 2024. In addition, the attacks are targeting a much larger geographic area. Israeli and Hezbollah attacks struck an average of 27–28 km from the Blue Line in the last week of September, up from an average of about 3–4 km between October 7, 2023, and August 31, 2024. The number of strikes and the geography of the conflict are likely to grow and include a larger swath of Lebanon and Israel as well as potentially Iran, Syria, Iraq, and Yemen.

Introduction

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.⁷