The leaders of the Sunni Arab jihadis waging war on Assad's government know Syria very well because they were once welcome guests:
One reason Islamic terrorists have been so successful at setting up operations in Syria was because a lot of those terrorists, or at least their leaders, had been in Syria before (as terrorists) and had come to know the country, and its terrorist resources, well. This was no accident. ...
After 2003, many of the terrorists hosted by the Assads were Sunni groups trying to overthrow the elected Shia government of Iraq.
I mentioned a week ago that I'd wondered (I won't go so far as to say predicted) if this would bite Assad in the end.
If we play our cards right, it will rather than just being a difficult period in his long rule.