Simplify the following text for a Grade 9 native English-speaking person.
Original: On September 27 the Army of the Three Guarantees entered Mexico City and the following day Iturbide proclaimed the independence of the Mexican Empire , as New Spain was to be henceforth called .
Simplified: On September 27 the Army of the Three Guarantees entered Mexico City . The next day Iturbide proclaimed the independence of the Mexican Empire .