The outbreak of the Revolution in 1910 began as a political crisis over presidential succession and exploded into civil wars of movement in northern Mexico and guerrilla warfare in the peasant centers near Mexico City. The former working relationship between the Mexican government and foreign and domestic enterprises was nearing an end with the fall of the Díaz government, producing uncertainty for businesses. The upstart challenger to Porfirio Díaz in the 1910 election, Francisco I. Madero, was from a very wealthy, estate-owning family in northern Mexico. After the fraudulent election, Madero issued the Plan of San Luis Potosí, calling for a revolt against Díaz. In his plan he made the vague promise to return stolen village lands, making Madero appear sympathetic to the peasantry and potentially bringing about land reform. For Mexican and foreign large-land owners, Madero's vague promise was a threat to their economic interests. For the peasants in Morelos, a sugar-growing area close to Mexico City, Madero's slowness to make good on his promise to restore village lands prompted a revolt against the government. Under the Plan of Ayala, sweeping land reform was the core of their demands. Earlier, the demands by the Liberal Party of Mexico (PLM) articulated a political and economic agenda, much of which was incorporated into the Constitution of 1917.