Under the orders of French Emperor Napoleon III, French troops arrive in Mexico in 1861 with a dual purpose: to help the Confederacy win the war against the United States and to conquer Mexico. As President Benito Juárez suspends payment of Mexico's foreign debts, the French drop their façade of debt negotiations and head for Puebla, where they are soundly defeated in their attempt to capture the city.

The French withdraw from their stunning setback and spend the summer of 1862 nursing their wounds and awaiting reinforcements in Orizaba. This gives the Mexicans ample time to highly fortify Puebla against a future attack. During spring of 1863 French troops head for Puebla and Mexico City in what they hope will be a pair of easy victories.

Juárez and his government flee Mexico City rather than trying to defend the capital against overwhelming odds. The French make their grand entrance and immediately encounter problems with the Catholic Church. Austrian Archduke Ferdinand Maximilian, asked by the French to become emperor of Mexico, will not accept the throne without a "popular" vote from the people.

When the American Civil War ends in 1865, out-of-work soldiers, generals and high-ranking officials from the former Confederate government drift into Mexico. General Ulysses S. Grant's U.S. Army is now free to stage maneuvers along the border, setting off panic in Mexico City and Paris. Grant's move prompts Napoleon III to cut his losses and pull his troops out. Now, it's only a matter of time before Mexican forces retake the country.