Hayat Tahrir al-Sham's leadership in Syria will likely embolden Islamists in both Lebanon and Jordan, while Syria's turbulent political transition will likely prompt another wave of refugees into both neighboring countries, encouraging jihadist groups, exacerbating political tensions and worsening security conditions there. On Dec. 15, the Syrian Islamist political and militant group Hayat Tahrir al-Sham, which led the rebels' advance that on Dec. 8 toppled the Syrian regime, established military control of Syria's main border crossings with Jordan and Lebanon. A day earlier, the general secretary of Lebanon's political and militant group Hezbollah, Naim Kassem, said the group had lost its supply route through Syria after the fall of Syrian President Bashar al Assad, but he added that Hezbollah "cannot judge [Syria's] new [HTS-led leaders] until they stabilise." Also on Dec. 14, Western and Israeli media outlets reported that the Jordanian military intelligence held secret talks with senior Israeli officials several days after the collapse of the Syrian regime to discuss jihadist threats in Syria, as well as Iranian attempts to smuggle weapons through Jordan to Palestinian militant groups in the West Bank. Reuters also reported on Dec. 13 that tens of thousands of Syrian refugees, largely members of minority sects like Shiites and Christians, have fled to Lebanon since the collapse of the Syrian regime for fear of persecution, despite HTS-led authorities' assurances of minorities' safety in Syria.

Lebanon and Jordan are concerned about a potential spillover from the Syrian regime's collapse and the ascent of an Islamist group to power in Syria. Several Lebanese political groups — including Sunni, far-right Maronite and Druze factions — celebrated the fall of Syria's al Assad regime. This caused concerns within the Lebanese government, specifically among some more moderate Sunni factions, Christians, and the Shiites led by Hezbollah and the Amal movement, that HTS' ascent to power in Syria could embolden Sunni Islamist and extremist groups in Lebanon. This worry is especially keen considering the presence of millions of Syrian refugees in Lebanon who are mostly Sunnis, the sectarian strife Lebanon experienced during the Syrian civil war, and the underlying threat of resurging jihadist sleeper cells amid the country's years-long political and economic crisis. Similarly, Jordan's government fears that an Islamist-led Syria could embolden domestic Islamist movements, such as the Muslim Brotherhood and Salafist-jihadist factions, particularly amid high anti-Israeli sentiment and rising support for the Islamic Action Front (a Muslim Brotherhood offshoot) in the latest parliamentary elections. Amman also fears that a turbulent political transition in Syria and an unstable security situation could result in another refugee influx toward Jordan, which would exacerbate these threats.

• Jordan and Lebanon host an estimated 1.3 million and 1.5 million Syrians, respectively, including registered and unregistered refugees. These substantial populations have caused social tensions and strained both countries' resources and infrastructure.
• Jabhat Fatah al-Sham, formerly known as Jabhat al-Nusra and later rebranded as HTS, launched attacks on Lebanon in the mid-2010s, particularly targeting border regions. These attacks led to intense battles with the Lebanese army and Hezbollah, both of which sought to expel the jihadist group from strategic areas on the Lebanon-Syria border. To this end, the Lebanese armed forces launched Operation Fajr al-Joroud in August 2017, which successfully cleared HTS militants from key areas in the Juroud Arsal region, ending their presence along the border and securing strategic high ground.
• During the Syrian civil war, the Islamic State carried out numerous attacks in Lebanon, particularly in border towns like Arsal, where it kidnapped and killed several security forces and civilians. In Jordan, the Islamic State launched high-profile assaults, including the 2016 Karak Castle shooting in which 11 Jordanian security forces and three civilians were killed, while 34 other individuals were injured. The group also used Jordan's border areas for recruitment and smuggling operations.
• Political factions in Lebanon, including Sunni groups like the Future Movement, Druze led by the Progressive Socialist Party, and certain Christian factions like the Lebanese Forces Party, opposed the al Assad regime due to its historical military occupation of Lebanon (1976—2005), alleged assassinations of anti-Syrian Lebanese political and media figures, and alleged role in fueling sectarian divisions and instability within the country.
• In Jordan's 2024 parliamentary elections, the Islamic Action Front secured 31 out of 138 seats, asignificant increase from the seven seats it held in the previous National Assembly. The party's growing popularity was due to its opposition to normalization with Israel amid widespread support for the Palestinians and frustration with Jordan's stance on the Israel-Hamas war.

Lebanon will likely face escalating political volatility as a weakened Hezbollah confronts a potential resurgence of Islamists and a political opposition emboldened by an HTS takeover of Syria, heightening the risks of sectarian violence. Lebanon is highly likely to face a period of political volatility over the next few months, as Hezbollah is increasingly concerned about the loss of its supply lines from Syria. The group's sense of encirclement will heighten its sensitivity to any threats, including political opposition and/or jihadist sleeper cells or remnants, both of which remain considerable risks to Hezbollah and Lebanon's stability. Lebanon will also become increasingly worried about a potentially aggressive Islamist Syrian regime, which would raise the likelihood of a jihadist resurgence in Lebanon, especially in poorer Sunni-dominated areas like West Bekaa, Akkar and Tripoli. Compounding this risk, the Lebanese army will struggle to maintain border stability, enforce the ceasefire between Hezbollah and Israel, and maintain internal security and cohesion. Meanwhile, Lebanese opposition forces —  particularly the far-right Christian Lebanese Forces — are likely to become politically more assertive in the face of a weakened Hezbollah, pushing for the Shiite militant group's disarmament and promoting a pro-Western or opposition presidential candidate. This will exacerbate the country's political crisis, possibly triggering sectarian violence. Finally, a turbulent political transition in Syria might prompt another large wave of refugees toward Lebanon, worsening economic strains in Lebanon and worsening sectarian tensions between various minority groups, including Maronite Christians.

• A limited armed conflict erupted May 7, 2008 in Beirut when Hezbollah clashed with government militias — mainly the Sunni Future Movement, and the Druze Progressive Social Party militias — after the then-pro-Western government back then attempted to dismantle Hezbollah's telecom network. Something similar could occur this time around, especially should opposition forces provoke Hezbollah again amid perceptions of its weakness.
• For the past few years, Hezbollah has supported Maronite Christian ally and head of the pro-Assad Marada party Suleiman Frangieh, while opposition forces have supported several pro-Western candidates, including former Minister of Finance Jihad Aoun and the Lebanese Armed Forces Cmdr. Joseph Aoun.
• Speaker of Parliament Nabih Berri scheduled a parliamentary session Jan. 9, 2025, to elect a new president. Lebanese media are reporting cautious optimism regarding the chances of electing a president during that session. Other sources have reported that Aoun — who enjoys Western and Arab country backing — has the best odds of winning.

Jordan will experience mounting domestic instability as growing Islamist influence, potential refugee influxes and heightened cross-border threats caused by a turbulent transition in Syria add strain to its security and economic resources, increasing the risk of anti-government unrest. Jordanians are unsatisfied with the government's response to the war in Gaza and will likely increasingly shift toward Islamist stances, as shown by the Islamic Action Front's popularity gains during the war. The group's rising popularity amid growing anti-Israel and pro-Palestinian sentiment, compounded by Islamist HTS leading Syria, will likely embolden Islamist actors domestically, eventually challenging Jordan's political balance and raising the likelihood of anti-government unrest. Should Syria's political transition become turbulent and the country remain fragmented amid factional fighting, another refugee influx into Jordan is likely. The additional economic strains would give extremist groups like the Islamic State opportunities to exploit. This also means that the porous Jordanian-Syrian border will remain vulnerable to infiltration by jihadist militants, armed groups and organized smuggling networks, increasing the risk of cross-border instability. Jordan will likely see renewed activity by pro-Iranian militias seeking to reestablish arms supply lines from Syria, through Jordan and toward the West Bank. These dynamics will likely exacerbate Jordan's domestic security situation, particularly if arms end up with Palestinians in refugee camps, or in the hands of jihadist, criminal and unfriendly tribal groups in Jordan. In the event of more social unrest, such groups could use these weapons against Jordanian authorities.

• Jordan maintained a firm diplomatic stance throughout the Gaza war, condemning Israeli actions and advocating for Palestinian rights. But many Jordanians criticized the stance as insufficient, demanding stronger measures. The Jordanian government did not take a stronger stance for fear of Israeli diplomatic reprisal and due to its concerns over Hamas as an Islamist group.