Iturbide marched into Mexico City on 27 September 1821 , his own birthday , with the Army of the Three Guarantees .
However , Iturbide had the advantage of having most of the former royalist army on his side .
Iturbide marched into Mexico City on 27 September 1821 , Iturbide 's own birthday , with the Army of the Three Guarantees .
However , Iturbide had the advantage of having most of the former royalist army on his side .