So let's outline a equivalent scenario. Mexico is taken over by a cartel terrorist gang as their government. The terrorists start launching rockets over the U.S border killing civilians in the U.S. Then one day the terrorists in Mexico invade the U.S., brutally kill thousands of our civilians and kidnap hundreds as hostages who are dragged back to Mexico.
Do you really think the U.S. military under direction of our government would not invade Mexico to stop the terrorism, end the rocket launches and attempt to get our citizens back?
Let's say the terrorists were using Mexican civilians as human shields and not allowing them to leave the conflict area. Do you really think this would cause the U.S. to re-think militarily invading Mexico to end the threat in the least bit?
Even if there were Mexican civilian casualties? We would do our best to minimize them but it would not change to focus to finish the job of completely eliminating the terrorists in Mexico.