The fall of the lengthy dictatorship of Porfirio Díaz in 1910 caused a massive power vacuum which was rapidly filled by armed revolutionary leaders. In 1920, once the most violent phase of the Revolution ended, military caciques became virtual lords of some states and some regions of Mexico. These cacicazgos became the foundations of an emerging political system. By the end of the 1930s, once the nation state consolidated its power, the regional bosses had to modernize or be eliminated. This article examines San Luis Potosí as a case study of that process.