The Second Federal Republic of Mexico (Spanish: Segunda República Federal de México) refers to the period of Mexican history involving a second attempt to establish a federal government in Mexico after the fall of the unitary Centralist Republic of Mexico in 1846 at the start of the Mexican-American War. It would last up until the Second French Intervention in Mexico led to the proclamation of the Second Mexican Empire in 1863.
The period of the Second Federal Republic prove to be one of the most eventful periods in Mexican history, experiencing two foreign invasions, the loss of half of the national territory, constitutional change, and a civil war. It was also a period of Mexican political evolution experiencing the downfall of the Conservative Party that had predominated during the Centralist Republic, and marking the rise of a Liberal Party hegemony which would consolidate itself throughout the rest of the century.
The Second Federal Republic was born in the first months of the Mexican-American War in 1846, with the restoration of the Constitution of 1824. The war ended in 1848 with Mexico being forced to cede half of its territory to the United States. The period immediately following the war would nonetheless be followed by a period of stable, moderate governments.
A Conservative coup then overthrew the government in 1852, bringing Santa Anna back for what would be his final dictatorship.
The Liberal revolt which in turn overthrew him in 1853, would inaugurate what would come to be known as La Reforma, a series of substantial unprecedented reforms in Mexican constitutional history, most notably the separation of church and state and the nationalization of Catholic Church lands. A new constitution implementing such measures was promulgated in 1857, upon which the Conservative Party opposition took up arms, inaugurating three years of what would come to be known as the Reform War.
The Liberal government led by president Benito Juarez would emerge triumphant in 1860, but a financial crisis led the government to postpone its external debts, a measure that was used as a pretext by the Second French Empire to launch an invasion of Mexico with the aim of turning it into a client state led by Maximilian of Habsburg. The Second French Intervention in Mexico began in 1861, but was subsequently delayed by a year due to the French loss in the Battle of Puebla. French reinforcements arrived and President Benito Juarez was forced to evacuate the capital which the French occupied by June, 1863. French troops subsequently arranged a Mexican Assembly of Notables to declare the establishment of the Second Mexican Empire in July 1863, putting an end to the era of the Second Federal Republic of Mexico.