From Rep. Joe Baca (D-CA) writing at the Huffington Post:

Had the French been victorious in that original Battle of Puebla on May 5th, 1862, they could have continued their influence across the Mexican nation, and would have likely supported the Confederacy in its battle against Union forces. Instead, the French had to regroup their forces and concentrate on their war with Mexico, which was much more united just one year after the first attack. Of course, just fourteen months after the Battle of Puebla, the U.S. Civil War would see a major battle when Union forces claimed victory at Gettysburg and effectively brought a close to the Civil War.

I guess nobody told General Sherman. And while I'll concede a rather weak grasp of Mexican military history, I'm pretty sure the French sacked the Mexican capital one year after that first attack--as in conquered the country and installed an emperor a month before the Battle of Gettysburg. Exit earmark proposal: $100,000 for remedial history courses for the esteemed and honorable members of the United States House of Representatives.