After the Mexican American War was won, some Americans at the time thought it would be a good idea to take all of Mexico, but most were happy to only take half.
The original goal had been to open a continental path from coast to coast, and that goal had been accomplished.
Why drag out the war longer, trying to subjugate a rebellious population? It would seem too much like brute aggression. One American newspaper proudly declared, “We take nothing by conquest. Thank God.”
“We never crossed a border. The border crossed us.” Saying of Tejanos (Texans of Mexican origin)