Treaty of Guadalupe Hildalgo

Drafted in 1848, the Treaty of Peace, Friendship, Limits and Settlement with the Republic of Mexico (AKA the Treaty of Guadalupe Hidalgo) marked the end of the war between the Republic of Mexico and the United States. This document establishes new borders between the two countries; a series of geographic, political, social, and legal boundaries that continue to be disputed to this day, often by New Mexicans within these borders. 

It is little surprise these disputes exist, as the document forced multiple nations to conform to disruptive legal and cultural constructs that affected their every way of life.