The Mexican state has been directly involved in education since the nineteenth century, promoting secular education. Control of education was a source of an ongoing conflict between the Mexican state and the Roman Catholic Church, which since the colonial era had exclusive charge of education. The mid-nineteenth-century Liberal Reform separated church and state, which had a direct impact on education. President Benito Juárez sought the expansion of public schools. During the long tenure of President Porfirio Díaz, the expansion of education became a priority under a cabinet-level post held by Justo Sierra; Sierra also served President Francisco I. Madero in the early years of the Mexican Revolution.