I’ve heard some ridiculous statements from people saying, usually sarcastically, that we should’ve annexed all of Mexico. Well, once it was clear, with the successful capture of Mexico City in 1847, that the Mexico had lost the war, was there any serious discussion in the US government or media to actually annex all of Mexico, and not just its northern territories like California and the Southwest? If so, what were the primary discussion points that were pro-all-annexation and pro-anti-all-annexation?
There may be more to say, but you might like to start with a discussion from the FAQ section "American Expansion" (in the app: about 25% of the way down the page). "During Manifest Destiny why did the US not try to annex all of Mexico and the rest of Central and South America?" , replies by /u/AlotOfReading .
But this is not to discourage discussion -- more questions, data, and debate are welcome.