This is important:
An unremarkable area of flat fields, orchards, farms and small villages lying between the Syrian town of Qusayr and Lebanon’s northern border has become a fiercely contested battleground that threatens to expand into Lebanon.
Fighters from Lebanon’s Shiite militant group Hezbollah and Syrian Army troops are fighting the rebel Free Syrian Army for control of an area that could become strategically significant if Damascus falls to the rebels and the regime of President Bashar al-Assad is forced to flee. Qusayr lies close to the highway that connects Damascus to Homs, Syria's third largest city, and then to Tartous, the coastal town which is a gateway to the mountain chain dominated by Alawites, an obscure offshoot of Shiite Islam that forms the backbone of the Assad regime.
Some analysts believe that if Assad is forced out of Damascus, the rump regime will decamp to the Alawite mountains to form an enclave that could survive on the logistical and material support of Iran, a key ally of the Assad regime and patron of Hezbollah.
I wrote earlier that Assad has motive to actually expand into Lebanon itself for a little more strategic depth.
And this would allow Syria to maintain links to Hezbollah once he doesn't have a land border from Syria into Lebanon via the main Damascus-to-Beirut highway, which was part of the basis for my original speculation that Assad should have contracted his realm to a core Syria stretching south to the Israeli and Jordanian borders. But Assad's ground forces are way too weak to hold that much ground now.
Assad needs foreign help to survive. So he needs to be just as big of a pain in the neck to us even if he can't rule all of Syria. So Assad needs a secure line of communication to Hezbollah in southern Lebanon. And that requires access to northern Lebanon as the first step to linking up with Hezbollah
