How can you tell?.................
The current violence in Mexico is a pale shade of a real civil war/ revolution. The last Mexican Revolution lasted 10 years, killed 1.3 million Mexicans (mostly civilians) over 500 Americans, and included a raid on Columbus, NM, a significant US punitive exhibition, and a sizable cross border firefight at Nogales, AZ.
If Mexico broke out into actual civil war, we would have to put a lot of troops on the border to secure it. A wall would not cut it. Tens of millions of Mexicans would seek to come north. Not to mention the likely spillover as people on this side of the border picked sides.
The human cost would be immense, the economic damage to Mexico incalculable, the cost to the US significant and it would make Syria look like a schoolyard scuffle.