i assume this is what was being referenced:

Matthew 28:

18 Then Jesus came to them and said, “All authority in heaven and on earth has been given to me. 19 Therefore go and make disciples of all nations, baptizing them in the name of the Father and of the Son and of the Holy Spirit, 20 and teaching them to obey everything I have commanded you. And surely I am with you always, to the very end of the age.”

no, he didnt specify america, but it is one of the more christian nations left in the world, i guess its not such a big leap of understanding from whats actually in the bible and the obvious suggestibility of many Americans; as we can see Mormonism exists in no small manner

while i agree that its not what should be happening, i think the most fault lies in the bible and not those specific Christians with this view