Final answer:
When Mexico gained independence from Spain in 1821, it was established as a constitutional monarchy under Agustín de Iturbide, with social and religious safeguards. Iturbide abdicated in 1823, leading to the creation of a republic. Subsequent territorial challenges included settler issues in Texas and loss of land after the Mexican-American War.
Step-by-step explanation:
Overview of Mexican Independence
After Mexico won its independence from Spain in 1821, significant political and social changes swept across the region. Agustín de Iturbide, a military leader who initially fought against the insurgents, later formed an alliance with the rebel leader Vicente Guerrero under the Plan de Iguala. This plan outlined the establishment of Mexico as a constitutional monarchy, with protections for the privileges of the creoles and the Catholic Church, social equality, and independence from Spain. Subsequently, Iturbide was proclaimed Mexico's first emperor.
The early years following independence were marked by a tremendous amount of political instability, with Iturbide abdicating in 1823 and Mexico becoming a republic. Furthermore, the new Mexican government faced challenges such as asserting control over its northern territories. To bolster settler numbers, it allowed 'Anglo' settlement from the United States into Texas, which later led to the Texas Revolution and the eventual cession of a vast swath of Mexican territory to the United States after the Mexican-American War.