Didn't say it did, GregF. We were talking about the Mexican Cession--the massive area that was ceded to the US in the Treaty of Guadalupe Hidalgo at end of the Mexican-American War-this acquisition did not include Texas--The Republic of Texas entered the Union as a slave state in 1845, after breaking away from Mexico in 1836(but you know that).
It is true that the war was connected to the claim that the Rio Grande was Texas' southern border--you can call that a land grab if you want (an arguable point because the population was mostly Anglo and self-identified as Texans), I don't want to fight about it, they all ready did that.