(In an earlier message) I informed you that ... I had ordered an efficient military force to take a position "between the Nueces and the Del Norte (Rio Grande)." This had become necessary, to meet a threatened invasion of Texas by the Mexican forces ... The invasion was threatened solely because Texas had determined ... to annex herself to our Union; and, under these circumstances, it was plainly our duty to extend our protection over her citizens and soil.

Question

(In an earlier message) I informed you that ... I had ordered an efficient military force to take a position "between the Nueces and the Del Norte (Rio Grande)." This had become necessary, to meet a threatened invasion of Texas by the Mexican forces ... The invasion was threatened solely because Texas had determined ... to annex herself to our Union; and, under these circumstances, it was plainly our duty to extend our protection over her citizens and soil.

... The Congress of Texas, by its act of December 19, 1836, had declared the Rio del Norte to be the boundary of that republic.... The country between that river and the Del Norte ... is now included within one of our congressional districts.... It became, therefore, of urgent necessity to provide for the defense of that portion of our country....
(On the 24th of April) a party ... of sixty-three men and officers, were ... dispatched from the American camp up the Rio del Norte, on its (North) bank, to ascertain whether the Mexican troops had crosses, or were preparing to cross, the river.... (They) became engaged with a large body of these (Mexican) troops, and, after a short affair, in which some sixteen (Americans) were killed and wounded, appear to have been surrounded and compelled to surrender....
We have tried every effort at reconciliation. The cup of forbearance had been exhausted even before the recent information from the frontier of the Del Norte. But now, ... Mexico has passed the boundary of the United States, has invaded our territory and shed American blood upon the American soil.

How does this document help answer the Mini-Q question: Was the United States justified in going to war with Mexico?

Answer 1

This document provides evidence that the United States was justified in going to war with Mexico. It explains that the Mexican forces had threatened to invade Texas, which had declared the Rio del Norte to be its boundary, and that the US had sent a military force to protect the region. It also explains that the US had tried every effort at reconciliation, but that Mexico had crossed the US boundary, invaded US territory, and shed American blood on American soil. This document thus provides evidence that the US was justified in going to war with Mexico.