I've never heard of a civil war where the Rebels had air power. If they did, surely they would be using stolen aircraft but that would mean they'd have the same fighters as the Empire. The Empire would not let some defense contractor create an entire fleet of fighters for the rebel alliance.

Was a neighboring empire/republic arming the Rebels? If so, why didn't they enter the conflict. Surely, the destruction of entire planets would call for intergalactic intervention, no?