The siege and humanitarian crisis in Gaza are worsening daily. Hundreds of Israeli airstrikes are estimated to be hitting Gaza every day. The timing of an anticipated Israeli ground incursion remains uncertain but would mark a new, more dangerous phase of the war and put more than a million Palestinians at grave risk. Concerns are mounting — both in the region and beyond — that war could expand, reportedly prompting Biden administration officials to prepare contingency plans for the evacuation of more than 600,000 Americans living in Israel and Lebanon.

USIP’s Mona Yacoubian discusses the risks of this war expanding to Lebanon and Syria, the potential for an even broader escalation with Iran and what it means for the United States.

What are the risks of this war expanding to two fronts with Lebanon and/or Syria?

Lebanon is the most dangerous second front. Concerns are mounting that the current war between Israel and Hamas could expand with the opening of a second front on Israel’s northern border with Lebanon. Cross-border clashes between Israel and the Iran-backed, Lebanese militant group Hezbollah alongside Palestinian armed factions have occurred almost daily since the October 7. The fighting has led to casualties in both Israel and Lebanon, including at least 40 Hezbollah fighters, and forced the evacuation of many communities on both sides of the border.  

Yet despite mounting tensions, Hezbollah does not appear to have an interest in widening the war at this time. Lebanon is already on its knees, contending with unprecedented economic, social and political crises that have essentially rendered the country a failed state. Meanwhile, the Israeli government has long warned that its response to a Hezbollah-provoked war would be wide-ranging and devastating. As such, Hezbollah is keenly aware that it cannot afford to bring further ruin on Lebanon, or it would dramatically undermine its domestic support base.

Instead, its calculus seems to hinge on portraying unity with Palestinian factions while harassing Israel with limited strikes designed to fulfill its “resistance” narrative without plunging into all-out war. Yet this strategy is extremely risky in the highly volatile environs of the Israel-Lebanon border. The potential is high for miscalculation that erupts into a full-scale conflict. As a reminder, the 2006 Israel-Lebanon war began with a Hezbollah cross-border raid and kidnapping of two soldiers, but quickly spiraled into a brutal war lasting 34 days.

Beyond the possibility of unintended escalation, Hezbollah could also change its calculus depending on the trajectory of the Israel-Hamas war. If Hamas is on the verge of total destruction, or if an Israeli ground incursion leads to massive civilian casualties, Hezbollah — perhaps compelled by Iran — could opt to widen the war and open a second front with Israel. Much would depend on the circumstances and the reaction by the Arab and Muslim “streets.”

Syria is already an active Israel-Iran conflict zone. Over the past several years, Syria has been the most active arena in the ongoing shadow war between Israel and Iran. Starting in 2017, the Israeli government opted to change its rules of engagement in Syria, accelerating and emboldening its strikes against Iranian proxies and key Syrian military targets. More recently, in May 2023, Israeli Defense Minister Yoav Gallant claimed to have doubled the number of Israeli strikes against Iranians in Syria.

Not surprisingly, these tensions have increased since October 7. Since the Hamas attack, Israel struck both the Damascus and Aleppo airports, in the latter case multiple times, temporarily disabling them. On October 24, Israel hit Syrian military targets in response to rocket launches from Syria toward Israel.  Ironically, Syria being such an active zone of Israeli-Iranian confrontation may diminish the prospects of a new front opening in Israel’s war against Hamas, given that significant kinetic activity between Israel and Iran already occurs in Syria, keeping the fight on the eastern side of Israel’s border.

Could such an expansion lead to an even broader escalation resulting in more direct Iranian involvement — and what would that mean for the United States?

Iran’s direct involvement in the war — either by its own decision or by Israel opting to strike Iran — is a nightmare scenario that would mark the transformation of the current conflict into a regional conflagration. Such a region-wide war would likely embroil Lebanon, Syria, Iraq and the Gulf. It would almost certainly also entail direct U.S. engagement. At this point, neither Iran nor Israel seems interested in pursuing this extreme option. Both countries likely calculate the massive destruction that would occur on all sides would be catastrophic for their own national interests and, in the case of Iran, even imperil regime survival. 

Nonetheless, Iran has exploited the conflict to reignite tensions with the United States through its various proxies. Iranian-backed forces have already unleashed a barrage of strikes on U.S. targets in Iraq and Syria, leading to at least 24 American troops injured in 13 attacks since October 17. Separately, on October 19, a U.S. navy warship operating in the Red Sea intercepted several missiles and drones fired by Houthi rebels in Yemen. U.S. officials openly worry that Yemen could get dragged into the conflict, jeopardizing the fragile steps underway to secure a cessation of hostilities.

The attacks end a six-month lull in Iranian proxy activity against U.S. targets. Concerned by the outburst of Iran-linked militia attacks on U.S. forces, U.S. Secretary of State Antony Blinken issued a stark warning to Iran at an October 24 U.N. Security Council meeting. He underscored that while the United States does not want to see the war widen and is not interested in direct conflict with Iran, the United States will defend its people “swiftly and decisively” if subject to attack. President Biden is reportedly weighing the need to respond to the attacks on U.S. forces to date against the threat of sparking a wider conflict, underscoring the delicate balance the administration faces in seeking to deter future attacks while not tipping the region into a wider conflagration.

The circumstances of the Israel-Hamas war over the coming days and weeks — its pace, conduct and trajectory — will determine whether the conflict remains contained to Israel and Gaza or whether it explodes into a much wider conflict.