The Republic of the Rio Grande was an independent nation that insurgents against the Central Mexican Government sought to establish in northern Mexico. The rebellion lasted from January 17 to November 6, 1840 and the Republic of the Rio Grande was never officially recognized; unlike their northern cousins, Texas, they never succeeded in their independence.
Red is The Republic, pink is disputed territories
Theoretically the land that the Republic operates could support it and like Texas, their rebellion could succeed, but how? What is the smallest change I can make to Mexico's history to allow for this republic to exist?