So long as the President of the United States is a real American, he will not invite invaders in. A significant majority of our military is conservative and pro-Constitution. If uninvited foreign intervention shows up, we will have the entire military on our side.
The big mess will most likely be on the purely civilian side, especially in dense cities. That is where most of the dying will happen, and I don’t think even the National Guard will be able to stop it.
Time to re-read Unintended Consequences.
Throwing these casualty figures around nonchalantly makes one sound like Bill Ayers. Remember he wanted 25 million Americans dead to install his Maoist dream. Things will change “hugely” after the November elections. We get two new USSC picks (also more Fed court picks!) and a few Trump Constitutional actions are upheld all this stuff will go away like air out of a balloon. There might be some inner city riots like Watts, etc. (Even then I don’t really think that will happen!). But that riot stuff has been handled before without resorting to “Civil War “! I really find all this Civil War talk tedious!