Simplify the following text for a Grade 11 native English-speaking person.
Original: After a distinguished career in the Austrian Navy , he was proclaimed Emperor of Mexico on 10 April 1864 during the Second Mexican Empire with the backing of Napoleon III of France and a group of Mexican monarchists who sought to revive the Mexican monarchy .
Simplified: After a distinguished career in the Austrian Navy he was proclaimed Emperor of Mexico , during the Second Mexican Empire .