The not so Civil war is what I'm referring to. That was American vs. American & not much different than the Kurds Saddam was oppressing. If Sherman had chemical weapons I'm sure he would've used them on his march to the sea.
I know, people will say "that's a stretch" & it is in a way; but Saddam Hussein ruled his country in the same way leaders all around the world have ruled for centuries. The U.S. govt. would do the same thing to it's own citizens if an entire community rose up, tried to kill the president & began open warfare against the govt's troops in the region. They would open fire. Not with with nuclear, chemical or biological weapons of course, but tanks & attack helicopters make people just as dead & the federal govt of the United States of America has shown on more than one occasion they will use the military to police the populace.
If you don't count the war of northern aggression as proof there are many, more modern instances where troops have been used with fatal consequences in more recent times. Kent state, Waco Tx., the Chicago high rise that was bombed with a concussion bomb an air natl guard plane that ignited gasoline stored on the roof & caused a big fire & killed several of the militants holed up inside (occurred in the 60's or early 70's iirc)
Then there are instance where the govt just ignored the posse comitatus act & used the army in the watts riots & then later in L.A in the aftermath of the Rodney King debacle; no one was killed by the military in those latter two instances to my knowledge but it could have easily happened.
I'm not saying any of those instances are right or wrong, but only proof that the president of the United States would authorize the putting down of insurrection inside this country by force of arms if it was deemed necessary up to & including killing 20,000 people. Saddam was a horrible man, but; he ruled the only way he could in that area & retain control...by force.