[clarification needed] Iturbide had formulated the Plan of Iguala in 1821, which united insurgents and royalist forces and Mexico's independence in September 1821.
The plan called for a constitutional monarchy, and when no European monarch presented himself as a candidate, the Mexican Congress proclaimed Iturbide as Emperor of Mexico in May 1822.
When a provincial delegation accepted the Plan de Casa Mata, it withdrew its allegiance from the imperial government and asserted sovereignty within its province.
Agustín de Iturbide was isolated without support outside of Mexico City and some factions of the army.
He reinstated the dissolved constituent Congress, abdicated the crown, and left the country in March 1823, for Italian exile with the promise of a 25,000 peso annual payment if he remained there.