Texas established an independent republic in 1836, throwing off Mexican rule. Its incorporation into the US was blocked by a home-grown independence faction, and American Republicans who were resistant to another pro-slavery state. However, President Polk was elected in 1844 on an expansionist platform, and promptly provoked war with Mexico to further his aims. In early 1846, American armies swiftly occupied the Disputed Territories east of the Rio Grande, then soundly defeated Mexican forces north of Matamoros before capturing Monterey in September. After defeat near Los Angeles on 8 January, Mexican forces in California swiftly capitulated. A string of Mexico’s Pacific ports, including Mazatlán, fell swiftly afterwards, and its main army was defeated at Buena Vista. When the capital, Mexico City, fell in September 1847, the Mexicans were forced to sue for peace: in the ensuing Treaty of Guadalupe Hidalgo, they conceded almost half their total land area to USA.
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