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After the successful War of Independence against the United Kingdom, the United States established its border with New Spain and what would become the Louisiana Purchase, a territory stretching mostly west of the Mississippi River. The Treaty of Fontainebleau in 1762 ceded what would become the Louisiana Purchase to Spain from France. However, in 1800 France regained the territory from Spain. Napoleon, although wanting to keep the territory to create an empire in North America, could not afford to hold the territory while fighting the United Kingdom and other states. His need for money led prompted the French to sell the territory to the United States in 1802. This effectively created the border with New Spain, what was then Mexico under Spanish rule, along what are now Texas, Oklahoma, Colorado, Wyoming, and Montana. This border stayed relatively stable for the next few decades. <ref>For more on the Louisiana Purchase, see: Rodriguez, J. P. (Ed.). (2002). <i>The Louisiana Purchase: a historical and geographical encyclopedia</i>. Santa Barbara, Calif: ABC-CLIO. </ref>

From 1810-1821, Mexico fought its own war of independence with Spain. Mexico succeeded in 1821 in establishing itself as an independent country that controlled what is mostly the Western United States and modern Mexico. The first few decades of Mexico's history were turbulent, as a struggle for power between conservatives, who wanted a centralized form of government, and liberals, who wanted a more federal system with more freedom for the states of Mexico. One early goal for Mexico was to stabilize its frontier regions, particularly in what is now Texas, which was officially called Coahuila y Tejas in Spanish. Mexico invited settlers to come to the region that was underpopulated, allowing settlers from the United States to arrive. Very soon, these settlers outnumbered Mexicans, called Tejanos, and native populations living in Texas. Armed hostility between the new, mostly Protestant settlers had increased over the years, with more Mexican troops now being stations in Texas. The Mexicans claimed the mostly white settlers refused to pay taxes, while the settlers had claimed the government to be corrupt. The first battle of what would become Texas' rebellion from Mexico took place at the Battle of Gonzales, although this was a relatively minor skirmish. In 1834-35, Santa Anna seized power in Mexico, who wanted to centralize control, where he suspended the Constitution of 1824. This caused a revolt in several provinces in Mexico, including Texas. Now, emboldened by Santa Anna's actions, a Texas independence movement led to the declaration of the Republic of Texas, an independent country, to be created. The Mexican army invaded Texas and after defeating and massacring rebels at the Alamo and other battles, Santa Anna himself was defeated at the Battle of San Jacinto, which led to his capture and being forced to sign a treaty that ended hostilities and ultimately gave Texas independence. Conflict The conflict between Mexico and the independent state of Mexico continued between 1836-1845. Part of the disputes were dispute was about the boundaries of the state, with Texans wanting areas covering what is now Western Texas and parts of surrounding states.<ref>For more on the history of Texas and Mexico during the early 19th century, see: Davis, G. (2002). <i>Land! Irish pioneers in Mexican and revolutionary Texas (1st ed)</i>. College Station: Texas A&M University Press. </ref>