Second Federal Republic of Mexico in the context of "Second Mexican Empire"

The Mexican–American War, also known in the United States as the Mexican War and in Mexico as the United States intervention in Mexico, (April 25, 1846 – February 2, 1848) was an invasion of Mexico by the United States. It followed the 1845 American annexation of Texas, which Mexico still considered its territory because it refused to recognize the Treaties of Velasco, signed by President Antonio López de Santa Anna after he was captured by the Texian Army during the 1836 Texas Revolution. The Republic of Texas was de facto an independent country, but most of its Anglo-American citizens who had moved from the United States to Texas after 1822 wanted to be annexed by the United States.

Sectional politics over slavery in the United States had previously prevented annexation because Texas would have been admitted as a slave state, upsetting the balance of power between Northern free states and Southern slave states. In the 1844 United States presidential election, Democrat James K. Polk was elected on a platform of expanding U.S. territory to Oregon, California (also a Mexican territory), and Texas by any means, with the 1845 annexation of Texas furthering that goal. However, the boundary between Texas and Mexico was disputed, with the Republic of Texas and the U.S. asserting it to be the Rio Grande and Mexico claiming it to be the more-northern Nueces River. Polk sent a diplomatic mission to Mexico in an attempt to buy the disputed territory, together with California and everything in between for $25 million (equivalent to $798 million in 2024), an offer the Mexican government refused. Polk then sent a group of 80 soldiers across the disputed territory to the Rio Grande, ignoring Mexican demands to withdraw. Mexican forces interpreted this as an attack and repelled the U.S. forces on April 25, 1846, a move which Polk used to convince the Congress of the United States to declare war.

In the history of Mexico, La Reforma (from Spanish: "The Reform"), or reform laws, refers to a pivotal set of laws, including a new constitution, that were enacted in the Second Federal Republic of Mexico during the 1850s after the Plan of Ayutla overthrew the dictatorship of Santa Anna. They were intended as modernizing measures: social, political, and economic, aimed at undermining the traditional power of the Catholic Church and the army. The reforms sought separation of church and state, equality before the law, and economic development. These anticlerical laws were enacted in the Second Mexican Republic between 1855 and 1863, during the governments of Juan Álvarez, Ignacio Comonfort and Benito Juárez. The laws also limited the ability of Catholic Church and Indigenous communities from collectively holding land. The liberal government sought the revenues from the disentailment of church property, which could fund the civil war against Mexican conservatives and to broaden the base of property ownership in Mexico and encouraging private enterprise. Several of them were raised to constitutional status by the constituent Congress that drafted the liberal Constitution of 1857. Although the laws had a major impact on the Catholic Church in Mexico, liberal proponents were not opposed to the church as a spiritual institution, but rather sought a secular state and a society not dominated by religion.

The Juárez Law reduced the power that military and ecclesiastical courts held. The Lerdo Law forced land held in collective ownership to be sold to individual owners. It aimed at creating a dynamic real estate market, creating a class of yeoman farmers owning their own land, and raising revenue for the state. The measure was intended to strip the Church of most of its property, as well as to break Indigenous communities' collective ownership of land.

The second French intervention in Mexico (Spanish: segunda intervención francesa en México), also known as the Second Franco-Mexican War (1861–1867), was a military invasion of the Republic of Mexico by the French Empire of Napoleon III, purportedly to force the collection of Mexican debts in conjunction with Great Britain and Spain. Mexican conservatives supported the invasion, since they had been defeated by the liberal government of Benito Juárez in a three-year civil war. Defeated on the battlefield, conservatives sought the aid of France to effect regime change and establish a monarchy in Mexico, a plan that meshed with Napoleon III's plans to re-establish the presence of the French Empire in the Americas. Although the French invasion displaced Juárez's Republican government from the Mexican capital and the monarchy of Archduke Maximilian was established, the Second Mexican Empire collapsed within a few years. Material aid from the United States, whose four-year civil war ended in 1865, invigorated the Republican fight against the regime of Maximilian, and the 1866 decision of Napoleon III to withdraw military support for Maximilian's regime accelerated the monarchy's collapse.

The intervention came as a civil war, the Reform War, had just concluded, and the intervention allowed the Conservative opposition against the liberal social and economic reforms of President Juárez to take up their cause once again. The Catholic Church, conservatives, much of the upper-class and Mexican nobility, and some indigenous communities invited, welcomed and collaborated with the French empire to install Maximilian as Emperor of Mexico. However, there was still significant support for republicanism in Mexico. Mexican society was most resistant to European models of governance, including monarchies, during and after the French intervention. The emperor himself however proved to be of liberal inclination and continued some of the Juárez government's most notable measures. Some liberal generals defected to the empire, including the powerful, northern governor Santiago Vidaurri, who had fought on the side of Juárez during the Reform War.

The United States of America was formed after thirteen British colonies in North America declared independence from the British Empire on July 4, 1776. In the Lee Resolution, passed by the Second Continental Congress two days prior, the colonies resolved that they were free and independent states. The union was formalized in the Articles of Confederation, which came into force on March 1, 1781, after being ratified by all 13 states. Their independence was recognized by Great Britain in the Treaty of Paris of 1783, which concluded the American Revolutionary War. This effectively doubled the size of the colonies, now able to stretch west past the Proclamation Line to the Mississippi River. This land was organized into territories and then states, though there remained some conflict with the sea-to-sea grants claimed by some of the original colonies. In time, these grants were ceded to the federal government.

The first great expansion of the country came with the Louisiana Purchase of 1803, which doubled the country's territory, although the southeastern border with Spanish Florida was the subject of much dispute until it and Spanish claims to the Oregon Country were ceded to the US in 1821. The Oregon Country gave the United States access to the Pacific Ocean, though it was shared for a time with the United Kingdom. The annexation of the Republic of Texas in 1845 led directly to the Mexican–American War, after which the victorious United States obtained the northern half of Mexico's territory, including what was quickly made the state of California.

The Plan of Ayutla was the 1854 written plan aimed at removing conservative, centralist President Antonio López de Santa Anna from control of Mexico during the Second Federal Republic of Mexico period. Initially, it seemed little different from other political plans of the era, but it is considered to be the first act of the Liberal Reform in Mexico. It was the catalyst for revolts in many parts of Mexico, which led to the resignation of Santa Anna from the presidency, never to vie for office again. The next Presidents of Mexico were the liberals, Juan Álvarez, Ignacio Comonfort, and Benito Juárez. The new regime would then proclaim the 1857 Mexican Constitution, which implemented a variety of liberal reforms.

The land which became the United States was inhabited by Native Americans for tens of thousands of years; their descendants include but may not be limited to 574 federally recognized tribes. The history of the present-day United States began in 1607 with the establishment of Jamestown in modern-day Virginia by settlers who arrived from the Kingdom of England, and the landing of the Mayflower by English pilgrims to Plymouth in 1620. In the late 15th century, European colonization began and largely decimated Indigenous societies through wars and epidemics. By the 1760s, the Thirteen Colonies, then part of British America and the Kingdom of Great Britain, were established. The Southern Colonies built an agricultural system on slave labor and enslaving millions from Africa. After the British victory over the Kingdom of France in the French and Indian Wars, Parliament imposed a series of taxes and issued the Intolerable Acts on the colonies in 1773, which were designed to end self-governance. Tensions between the colonies and British authorities subsequently intensified, leading to the Revolutionary War, which commenced with the Battles of Lexington and Concord on April 19, 1775. In June 1775, the Second Continental Congress established the Continental Army and unanimously selected George Washington as its commander-in-chief. The following year, on July 4, 1776, the Second Continental Congress unanimously declared its independence, issuing the Declaration of Independence. On September 3, 1783, in the Treaty of Paris, the British acknowledged the independence and sovereignty of the Thirteen Colonies, leading to the establishment of the United States. On September 17, 1787, the U.S. Constitution was signed by a majority of delegates, and was later ratified by the Thirteen Colonies, leading to the first modern U.S. government.

In the 1788-89 presidential election, Washington was elected the nation's first U.S. president. Along with his Treasury Secretary, Alexander Hamilton, Washington sought to create a relatively stronger central government than that favored by other founders, including Thomas Jefferson and James Madison. On March 4, 1789, the new nation debated, adopted, and ratified the U.S. Constitution, which is now the oldest and longest-standing written and codified national constitution in the world. In 1791, a Bill of Rights was added to guarantee inalienable rights. In 1803, Jefferson, then serving as the nation's third president, negotiated the Louisiana Purchase, which doubled the size of the country. Encouraged by available, inexpensive land, and the notion of manifest destiny, the country underwent westward expansion in a project of settler colonialism marked by a series of conflicts with the continent's indigenous inhabitants. The most notable advocate of manifest destiny was President James K. Polk, who annexed Texas in 1845, and declared war on Mexico the next year. An overwhelming U.S. victory in the Mexican-American War led to the Treaty of Guadalupe Hidalgo in 1848, where the U.S. acquired much of the American Southwest from Mexico. Whether or not slavery should be legal in the expanded territories was an issue of national contention, and led to increasing tensions over slavery.