It’s because they may have just saved the Union’s ass in the Civil War, that’s why!
In 1862, England, Spain and France sent forces to Mexico to collect debts. The French wanted more than that, though. They wanted to stick around. So, they sent their forces toward Mexico City to install Maximilian of Austria as ruler. On May 5, at Puebla (100 miles east of Mexico City), an outnumbered force of Mexican soldiers and farmers handed the French army their first defeat in 50 years.
Why do we care?
France hated Lincoln and the U.S. If they had won, they would have supported the South in the Civil War and would have used Mexico to supply the Confederates. In fact, the French sent a larger force after the defeat at Puebla and managed to put Maximilian in Mexico City the next year. But the president of Mexico, Benito Juarez, fled north and with the help of Californian and Texan citizens, he managed to hold off the French until the U.S. was reunited. The U.S. then helped Juarez toss out Maximilian.
Hey! Who the hell let Paul Harvey in here?