What cause the Mexican-American war?

(1846-8), the first successful international war of USA 'manifest destiny' imperialism, in which Pres Polk provoked a border dispute in order to seize the New Mexico territory (all of today's south-western states) and California. Mexico had not accepted the independence of Texas, still less its claim to the strip between the Nueces river and the Rio Grande. Following American annexation of Texas in early 1845, a US army of 'observation' under Taylor moved from Louisiana to the Nueces strip. In May 1846, 3, 700 Mexicans attacked Taylor's 2, 300. Repulsed at Palo Alto and defeated at Resaca de la Palma, they fell back behind the Rio Grande. The USA declared war on the 13th.  more