There is a new effort emerging In Mexico to nullify a treaty that allowed the United States to annex most of Mexico’s historic territory – what is now Texas, Arizona, New Mexico and California. As KUT Public Radio reports, backers of the effort to nullify the Treaty of Guadalupe Hidalgo – which Mexican officials were forced to sign in 1848 at the close of the Mexican-American War – argue that the treaty violates now-accepted international legal norms, and therefore is invalid. A lawsuit filed by the group could potentially reverse the treaty and return the land to Mexico.