Mexico and America found themselves in a standoff after the Texas Annexation. Texas had a signed treaty that recognized their borders out to the Rio Grande River. Mexico declared that treaty null and void due to Santa Anna being a captive at the time he signed it. Furthermore, even if this self-proclaimed Texas was independent, which it was not, the Nueces River was the border of the rebellious Province of Tejas, not the Rio Grande. America sent a diplomatic mission to Mexico seeking to deal with the mutual misunderstanding of the where the border was the old fashioned way. Money. America would buy the disputed territory at what it considered a fair market value. The Mexicans sent the diplomatic mission away with a message to stay out of Mexican lands or risk war. America, with their typical respect for the demands of others, gave Mexico the proverbial middle finger, and promptly went down to the mouth of the Rio Grande to build a border fort on the Texas side of the river.