What historical document was signed on September 27, 1821?

The historical document signed on September 27, 1821, is the Declaration of Independence of the Mexican Empire. This declaration marked the culmination of a protracted struggle for independence from Spanish colonial rule, which began in the early 19th century. The successful capture of Mexico City by insurgent forces led by figures such as Agustín de Iturbide was a significant moment in the Mexican War of Independence, solidifying Mexico's transition from a colony to an independent nation.

The Declaration established Mexico as an empire, emphasizing national sovereignty and self-determination. It represented a turning point in history, signifying the end of Spanish colonial dominance in the region and the birth of a new nation with its distinct identity. Iturbide later became emperor, reflecting the ambitions of the new leadership at that time.

In contrast, the other options represent different contexts and timeframes in Mexican history. The Proclamation of Independence might refer to various independence movements but is not specifically tied to the events of 1821. The Treaty of Guadalupe Hidalgo was signed in 1848 and concluded the Mexican-American War, while the Constitution of the Mexican Empire came later, establishing the structure of government after independence was achieved. Understanding these distinctions helps clarify the significance of the Declaration