Before Texas was a state, or even a US territory, it was part of Mexico, the province of Coahuila Tejas. Mexico itself initially was a Spanish possession, New Spain, and after 1692 the Spanish Crown sent an army into the Rio Grande region and California to establish a buffer zone between New Spain and surrounding French, British, and Russian territories. Along with Catholic missions, the Spanish built forts there, including one in San Antonio (the Alamo) and one in San Francisco (the Presidio). By the early 1800s, however, the Spanish state was crumbling economically and politically, and Mexican nationalists, together with France, succeeded in ousting Spain and gaining independence (1821). A period of instability and internal conflict in Mexico ensued, during which Anglo settlers in Texas recruited more of their own with an eye toward setting up a free state, which they proclaimed in 1835. They established the independent Republic of Texas a year later, after a brief, but bloody, war with Mexico.

Before Texas was a state, or even a US territory, it was part of Mexico, the province of Coahuila Tejas. Mexico itself initially was a Spanish possession, New Spain, and after 1692 the Spanish Crown sent an army into the Rio Grande region and California to establish a buffer zone between New Spain and surrounding French, British, and Russian territories. Along with Catholic missions, the Spanish built forts there, including one in San Antonio (the Alamo) and one in San Francisco (the Presidio). By the early 1800s, however, the Spanish state was crumbling economically and politically, and Mexican nationalists, together with France, succeeded in ousting Spain and gaining independence (1821). A period of instability and internal conflict in Mexico ensued, during which Anglo settlers in Texas recruited more of their own with an eye toward setting up a free state, which they proclaimed in 1835. They established the independent Republic of Texas a year later, after a brief, but bloody, war with Mexico.

More white settlement in Texas followed. By the 1840s, Texas leaders were pressing for US statehood, and they achieved this through an act of Congress in 1845. However, the annexation of Texas riled Mexico, which—despite the interregnum of Texas’s free-state status—still considered the province its own. War broke out between the United States and Mexico in 1846, lasting until 1848. The victor was the United States, which demanded additional territorial concessions from Mexico in the Treaty of Guadalupe Hidalgo (1848). With this treaty, not only Texas, but most of the rest of what is now the southwestern United States, including California, was ceded to the US government.