“How fatal that man will be to France!” a Spanish general predicted in a Nov. 9, 1862 letter to a friend in Paris.
It did not take a seer to see that Alphonse Dubois would make a mess of things in Mexico like he had two decades earlier in Texas. He was, after all, the devious diplomat responsible for the infamous “Pig War.”

Alphonse Dubois began his checkered career in the French foreign service at the age of 22. Eight years later in 1839, the low man on the embassy totem p...