Some historians have argued that France's real goal was to help break up the American Union, at the time in the midst of a civil war, by helping the southern Confederacy.
Donald W. Miles states, "At the time, there were fears in the United States that the French would use Mexico as a base to back the Confederacy, so President Lincoln and his Secretary of State went out of their way to appear 'neutral' in the Mexican situation. They did not want to take on the French and the Confederates at the same time".[31] Dr. Miles goes on to explain that "Napoleon III had hesitated to take on the United States directly, but now the news of the Civil War changed everything".[32] It meant that the Americans would be occupied with their conflict between North and South for some time. Upon hearing the Spaniards and the British had sailed off to grab the customs house in Veracruz to start collecting their duties, Napoleon decided he would not only send the French navy, but would also start looking for someone to place as emperor in Mexico. He would then use Mexico as a base to help the Confederates win their war against the United States. Napoleon saw this as an opportunity not to be missed.[32]
Historian Justo Sierra has written in his Political Evolution of the Mexican People, that had Mexico not defeated the French in Puebla on May 5, 1862, France would have gone to the aid of the South in the U.S. Civil War and the United States' destiny could have been very different.[33][34]
Ignacio Gonzalez wrote, "Some scholars, including José Antonio Burciaga, believe that had the French defeated México at Puebla, France would have aided the South in the American Civil War in order to free Southern ports of the Union Blockade. During this time, Confederate General Robert E. Lee was enjoying success, and French intervention could have had an impact on the Civil War."[22]
