France's goal was to help break up the American Union, at the time in the midst of a civil war, by helping the southern Confederacy: "The Mexicans had won a great victory that kept Napoleon III from supplying the confederate rebels for another year, allowing the United States to build a powerful army. This grand army smashed the Confederates at Gettysburg just 14 months after the battle of Puebla, essentially ending the Civil War."