After France recalled its ambassador from Washington last September to protest a submarine deal between Australia, the United Kingdom, and the United States, many remarked that we had reached the lowest point in Franco-American relations since the 1790s. In some ways this is true, but Edward Shawcross reminds us of an even more dangerous moment and offers a warning for our foreign policy class in his engaging new book, The Last Emperor of Mexico.

That emperor was Maximilian, the artistically minded second son of the Austrian Habsburgs. He had capably administered the Austrian Navy and a province in Italy but had been replaced because he disapproved of his older brother Franz Joseph's autocratic tendencies.

In Mexico, meanwhile, conservatives were willing to give monarchy a chance, having...