Between November 2013 and April 2014, the Syrian government carried out a massive Hezbollah-backed offensive against the rebel-controlled territory around Damascus. Through this, Damascus mostly eliminated the pocket of rebels, driving them further north within Syria or into Lebanon. Significant rebel formations, however, remained, especially the town of al Zabadani near the border with Lebanon in the southern Qalamoun region.
These remaining rebels are weak and under continuous pressure from Assad loyalists and Hezbollah. Damascus has not yet pacified this region and rebels cling on in the uplands and mountain passes. Hezbollah and the Lebanese army have set up a number of checkpoints, but the border is still extremely porous. From these bases, rebels have successfully ambushed both Syrian government and Hezbollah units. These ambushes increased when Damascus withdrew a significant portion of its main combat formations for deployment elsewhere.
Rebels have also been particularly active in the north near Arsal, where they have taken Lebanese army and security personnel captive in raids and ambushes. Many of these rebels are Jabhat al-Nusra fighters, but the Islamic State has increased its presence significantly, beefed up by former Jabhat al-Nusra members. Unlike elsewhere in Syria, these two groups have been cooperating, mainly because of their extremely weak position.
Anti-government forces in Qalamoun are focusing their efforts on sustaining their raids into Lebanon and on surviving the winter. Raids can be continued because rebel groups remain small and nimble and the border porous. These incursions enable the rebels to maintain some momentum and initiative, which inflicts losses upon their opponents and disrupts and prevents their opponents from isolating them. Raids also yield tangible results, such as prisoners and hostages the rebels can then barter for concessions.
Surviving the winter means maintaining supply levels. Militant attacks have focused on opening up a route from Lebanon into the Qalamoun to bring much-needed supplies. In the near-term, however, rebels have chosen to consolidate their positions in eastern Qalamoun, which has access to supply routes leading from Homs and the Syrian desert. This strategy becomes increasingly important as the Syrian government readies a fresh offensive.
In the long-term, Islamic State leaders are trying to gain traction with Lebanon's Sunni population with the goal of sparking local Sunnis to start a conflict similar to that in Iraq. Bringing Lebanon into the wider Syrian civil war would bolster the overwhelmingly Sunni rebel position, especially by forcing Hezbollah to redirect its efforts to Lebanon instead of Syria.
On their own, Syria's rebels will not be able to take control of territory inside of Lebanon. Their numbers are low in the Qalamoun region — credible estimates set them at around 3,000 spread over a vast region. They simply do not have the manpower required to seize and occupy new terrain for long durations, something clearly demonstrated by failed attempts earlier in 2014. Blockades have further weakened them by eroding their supply base. Rebels will continue to be able to conduct significant raids into Lebanon, but not offensives to capture and hold towns or cities.
In order to push into Lebanon, rebels would first need to receive reinforcements from elsewhere in Syria, requiring them to move troops down the M5 highway. This route divides Qalamoun from eastern Syria where the bulk of the rebel forces are located. Government forces, however, monitor the highway closely.
Instead, the greatest threat to Lebanon is domestic upheaval on the part of Lebanese Sunnis. There have been continued tensions and fighting in Tripoli between the Sunni residents and the army as well as the Alawite community. Reports also indicate increasing numbers of Islamic State sleeper cells in Tripoli and Akkar preparing for an opportune moment to carry out attacks. Qalamoun-based rebels could also work to promote an uprising by continuing cross-border raids that divert Lebanese security resources and inspire Lebanese Sunni populations to conduct attacks.
The threat of a large offensive by Syrian rebels along the Lebanese border remains, for the time being, a minor one. In spite of their intentions, these forces do not have the strength, numbers or supplies to make a play at a repeat of Islamic State successes in Iraq. Instead, they will continue to mount low-level raids and harass their opponents with guerrilla tactics while attempting to spark a Lebanese Sunni uprising — two actions that are already posing challenges for Lebanon's government.