If we were going to have foreign intervention in a US, bullets flying, civil war, I suspect it'd be like Iran was involved with the war in Iraq. That is no uniformed troops on our soil or planes in our air, but ammo and spicy playdoh would suddenly be pretty easy to find, and there may be some really fit guys that like vodka willing to show the III percenters and Antifa how to make neat things.
Why risk your troops, or worse, unifying us again, when we'll kill each other.