Centralist Republic of Mexico in the context of "Thornton Affair"

The First Mexican Republic, known also as the First Federal Republic (Spanish: Primera República Federal), existed from 1824 to 1835. It was a federated republic, established by the Constitution of 1824, the first constitution of independent Mexico, and officially designated the United Mexican States (Spanish: Estados Unidos Mexicanos, listen). It ended in 1835, when conservatives under Antonio López de Santa Anna transformed it into a unitary state, the Centralist Republic of Mexico.

The republic was proclaimed on 1 November 1823 by the Supreme Executive Power, months after the fall of the Mexican Empire ruled by emperor Agustin I, a former royalist military officer-turned-insurgent for independence. The federation was formally and legally established on 4 October 1824, when the Federal Constitution of the United Mexican States came into force.

Antonio de Padua María Severino López de Santa Anna y Pérez de Lebrón (21 February 1794 – 21 June 1876), often known as Santa Anna, was a Mexican general, politician, and caudillo who served as the 8th president of Mexico on multiple occasions between 1833 and 1855. He also served as vice president of Mexico from 1837 to 1839. He was a controversial and pivotal figure in Mexican politics during the 19th century, to the point that he has been called an "uncrowned monarch", and historians often refer to the three decades after Mexican independence as the "Age of Santa Anna".

Santa Anna was in charge of the garrison at Veracruz at the time Mexico won independence in 1821. He would go on to play a notable role in the fall of the First Mexican Empire, the fall of the First Mexican Republic, the promulgation of the Constitution of 1835, the establishment of the Centralist Republic of Mexico, the Texas Revolution, the Pastry War, the promulgation of the Constitution of 1843, and the Mexican–American War. He became well known in the United States due to his role in the Texas Revolution and in the Mexican–American War.

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 Republic of Texas was the only state to enter by treaty into the United States and admitted to the Union as the 28th state on December 29, 1845.

The Republic of Texas declared independence from the Republic of Mexico on March 2, 1836. It applied for annexation to the United States the same year, but was rejected by the United States secretary of state, John Forsyth, under President Andrew Jackson. At that time, the majority of the Texian population favored the annexation of the Republic by the United States. The leadership of both major U.S. political parties (the Democrats and the Whigs) opposed the introduction of Texas – a vast slave-holding region – into the volatile political climate of the pro- and anti-slavery sectional controversies in Congress. Moreover, they wished to avoid a war with Mexico, whose government had outlawed slavery and refused to acknowledge the sovereignty of its rebellious northern province. With Texas's economic fortunes declining by the early 1840s, the president of the Texas Republic, Sam Houston, arranged talks with Mexico to explore the possibility of securing official recognition of independence, with the United Kingdom mediating.

The Texian Army, also known as the Revolutionary Army and Army of the People, was the land warfare branch of the Texian armed forces during the Texas Revolution. It spontaneously formed from the Texian Militia in October 1835 following the Battle of Gonzales. Along with the Texian Navy, it helped the Republic of Texas win independence from the Centralist Republic of Mexico on May 14, 1836 at the Treaties of Velasco. Although the Texas Army was officially established by the Consultation of the Republic of Texas on November 13, 1835, it did not replace the Texian Army until after the Battle of San Jacinto.

The Texas Revolution (October 2, 1835 – April 21, 1836) was a rebellion by Anglo-American immigrants as well as Hispanic Texans (known as Texians and Tejanos respectively) against the centralist government of Mexico in the Mexican state of Coahuila y Tejas. Although the uprising was part of a larger revolt against the Centralist Republic of Mexico that included other provinces opposed to the regime of President Antonio López de Santa Anna, the Mexican government believed the United States had instigated the Texas insurrection with the goal of annexation. The Mexican Congress passed the Tornel Decree, declaring that any foreigners fighting against Mexican troops "will be deemed pirates and dealt with as such, being citizens of no nation presently at war with the Republic and fighting under no recognized flag". Only the province of Texas succeeded in breaking with Mexico, establishing the Republic of Texas. It was eventually annexed by the United States about a decade later.

The Republic of Texas (Spanish: República de Tejas), or simply Texas, was a sovereign country in North America from March 2, 1836, to February 19, 1846. Texas was bordered by Mexico to the west and southwest, the Gulf of Mexico to the southeast, the two U.S. states of Louisiana and Arkansas to the east and northeast, and U.S. unorganized territory encompassing parts of the current U.S. states of Oklahoma, Kansas, Colorado, and Wyoming to the north. The Texas Revolution began when hostilities broke out on October 2, 1835, shortly before the regime of Mexican President and General Antonio López de Santa Anna adopted a new Mexican constitution known as the Siete Leyes that abolished the authority of the states under the federal republic and established a centralized government. The revolution lasted for over six months. On March 2, 1836, delegates in convention proclaimed the Texas Declaration of Independence. Major fighting ended on April 21, 1836, with the Treaties of Velasco that ended the fighting and secured Texas' independence.

The Mexican Congress refused to recognize the independence of the Republic of Texas, as the Treaties of Velasco were signed by Santa Anna under duress as prisoner. The majority of the Mexican Congress did not approve the agreement. Much of its territory was controlled and disputed by Mexico or the Comancheria; Mexico considered it a rebellious province during its entire existence. The Anglo-American residents of the area and of the republic were referred to as Texians, while Texans of Mexican descent were referred to as Tejanos.