Excerpts from Books and Wikipedia
"In 1862, the country was invaded by France which sought to collect debts that the Juárez government had defaulted on, but the larger purpose was to install a ruler under French control. . . . Archduke Ferdinand Maximilian of Austria was installed as Emperor Maximilian I of Mexico, with support from the Catholic Church, conservative elements of the upper class, and some indigenous communities. Although the French suffered an initial defeat (the Battle of Puebla on May 5, 1862, now commemorated as the Cinco de Mayo holiday), the French eventually defeated the Mexican army and set Maximilian on the throne. . . . France never made a profit in Mexico and its Mexican expedition grew increasingly unpopular. Finally in the spring of 1865, after the US Civil War was over, the US demanded the withdrawal of French troops from Mexico. Napoleon III quietly complied." [Wikipedia] "Benito Juárez returned to Mexico City as president. Mexican conservatives had utterly disgraced themselves by inviting the French invasion. They would never again rule Mexico. Nor would Catholicism ever regain its former prominence in Mexican society."