-After Achieving Independence from Spain in 1821, Mexico's Chief Concern

-After achieving independence from Spain in 1821, Mexico's chief concern was securing its northern border with the United States, which was addressed by _.

A) offering land grants in Texas to Americans who agreed to follow Mexican laws
B) adopting the mission system in California and New Mexico to convert Indians to Christianity
C) creating military alliances with the Apache and Comanche, who dominated that region
D) relocating Mexican settlers from the interior to this region