The Mexican War (1846-1848) and Internal Colonialism
The Liberty Party in 1837 was the first political party that was antislavery. It ran James E. Burney for President. Burney is a paradoxical figure reflective of the rapid rise of abolitionism. He was a native born Alabaman and a former slaveowner. The Liberty Party changed during the Mexican party and merged into the Free Soil party in 1848 directly in response to war with Mexico. Their platform was devoted to keeping the West free of slaves and slave labor systems.
The expansion of Anglo Americans interested in acquiring new land grants from the Mexican government through empresarios began in the 1820s when figures like Stephen F. Austin began to settle in Texas. Austin and some early prominent Anglo American settlers were granted large land grants by the Mexican state in exchange for recruiting and managing American settlers into Texas. The history of this is admirably analyzed in Andrés Reséndez, Changing National Identities at the Frontier: Texas and New Mexico, 1800-1850. (Cambridge University Press, 2004). Reséndez, shows that the reliance, cooperation and ultimately rivalry between Anglos and Mexicanos from the 1820s through the 1840s is far more complex than the simple narrative of pioneers and rise of the Republic that dominated the older histories of this period.
Andrés Reséndez, Changing National Identities at the Frontier: Texas and New Mexico, 1800-1850. (Cambridge University Press, 2004)
Mexican National Archives (has links that are useful to research 19th century Mexican and Mexican-American history