this leading one here, is that at least 40,000 of that total is Assad forces or militias supporting him. Militia fighting him--and non-combatants (killed by both sides)--make up the rest. In fact, not a single report or count, even by the Assad opponents and groups friendly to him, endorse the 100,000 figure.
But don't let the facts get in the way of the first air strike. Assad is bad enough but the propaganda--from Kerry to certain MSNBC folks--just shows the weakness in their case.