It is time for opposition to the Annexation of Texas to cease.... Texas is now ours.... Let their reception into the "family" be frank, kindly, and cheerful (O)ther nations have undertaken ... hostile interference against us, ... h pering our power, limiting our greatness and checking the fulfillment of our manifest destiny to overspread the continent allotted by Providence (God) for the free development of our yearly multiplying millions.

Question

It is time for opposition to the Annexation of Texas to cease.... Texas is now ours.... Let their reception into the "family" be frank, kindly, and cheerful (O)ther nations have undertaken ... hostile interference against us, ... h pering our power, limiting our greatness and checking the fulfillment of our manifest destiny to overspread the continent allotted by Providence (God) for the free development of our yearly multiplying millions.

California will, probably, next fall away from (Mexico).... Imbecile and distracted, Mexico never can exert any real governmental authority over such a country... The Anglo-Saxon foot is already on (California's) borders.... ?
armed with the plough and the rifle, and marking its trail with schools and colleges. courts and representative halls, mills and meeting-houses.... All this (will happen) in the natural flow of events...

How can this document be used to justify America’s going to war with Mexico?

Answer 1

This document can be used to justify America's going to war with Mexico by emphasizing the idea of Manifest Destiny and the idea that Mexico is too weak to exert any real governmental authority over California. It suggests that the "Anglo-Saxon foot" is already on California's borders and that the natural flow of events will lead to the spread of American culture and values. This implies that Mexico is a threat to America's destiny and that war is necessary to protect America's interests.