The USA did purchase the mexican terriory.

www.en.wikipededia.org/wiki/mexican_american_war

www.en.wikipededia.org/wiki/treaty_of_Guadalupe_Hidalgo

I guess our president hasnt a CLUE about when the USA bought the mexican territory. It is a SHAME that he doesnt even read the history books, and he makes things and rules up as he goes.