Key moments in Mexican political history

--1910: Autocrat Porfirio Diaz, in power for 35 years, rigs presidential election, creating anger that sets off decade-long civil war in which hundreds of thousands die.

--1929: President Plutarco Elias Calles moves to end continuing political turmoil by bringing Mexico's feuding factions into a single organization that is eventually named the Institutional Revolutionary Party, or PRI, that he dominates. Fraudulent election that year sets oft-followed precedent.

--1936: President Lazaro Cardenas rebels against Calles' control, forcing him into exile and establishing a system in which presidents surrender their power at the end of a six-year term after choosing their own successor and rigging elections, if necessary, to assure PRI victory.

--1939: Political and religious conservatives join with reformers to create the small National Action Party.

--1946: Opposition parties are allowed token presence in Congress.

--1953: Women get right to vote.

--1988: PRI uses fraud to defeat a challenge by leftist coalition that splits off to become the Democratic Revolution Party. Questions about legitimacy lead government to allow a series of election reforms.

--1989: PRI allows opposition candidate to win governorship for first time.

--1990: Autonomous Federal Elections Institute created, taking role of organizing elections away from federal government.

--1997: PRI loses absolute majority in Congress for first time.

--2000: National Action Party's Vicente Fox wins presidency, ending 71 years of PRI control.

--2012: PRI's Enrique Pena Nieto apparently wins election, recovering presidency for his party.