When they started recieveing thier cheque from Blackwater, a outfit providing mercs do the government. Read it on their website, no one is hiding the fact.
There are also allegations that they were CIA, but I won't get into that at the moment. "Innocent civilians" are not armed, nor are they escorting military equipment and supplies.
They were mercs, or are you naive enough to be fooled by a simple name-change. A rose by any other name...
edit: Right, I forgot. If someone were to invade America, that would be completely legal, right? Sorry, but there is a such a thing as international law. You know, Geneva Convention, Nuremberg...that stuff. Invading a foreign nation is illegal, how can it not be?