1833年到1855年间由圣塔安那执政（Santa Anna），他的政治生涯几经起伏更迭，下朝再上朝，共有11次之多。这段期间墨西哥和美国几番激战，最后割让了德州、新墨西哥州和亚历桑那州给美国。 1855年，曾被圣塔安那放逐的政敌杰瑞兹（Benito Juarez）结合强大的反对势力，把执政十多年的独裁者赶下台。杰瑞兹属自由新政派，在位时推动新法，取消天主教会和军队的免责权。这些保守势力的反弹导致改革战争（War of the Reform），这是有史以来最血腥的一次内战，但最终结果还是代表自由派的杰瑞兹再度赢得选举。再度执政的杰瑞兹虽然面对国内外动荡情势，仍致力于基础建设、推展教育，慢慢使墨西哥的政治社会环境步上正轨。
In 1855, Santa Anna, who had become leader one more time, was overthrown by the liberals, in what was called the Revolution of Ayutla. The moderate liberal Ignacio Comonfort became president. The Moderados tried to find a middle ground between the nation's Liberals and Conservatives.
The 1857 Constitution
During Comonfort's presidency, a new Constitution was drafted. The Constitution of 1857 retained most of the Roman Catholic Church's Colonial era privileges and revenues, but, unlike the earlier constitution, did not mandate that the Catholic Church be the nation's exclusive religion. Such reforms were unacceptable to the leadership of the clergy and the Conservatives. Comonfort and members of his administration were excommunicated, and a revolt was then declared.
The War of Reform
This led to the War of Reform, from December 1857 to January 1861. This civil war became increasingly bloody and polarized the nation's politics. Many of the Moderates came over to the side of the Liberals, convinced that the great political power of the Church needed to be curbed. For some time, the Liberals and Conservatives had their own governments, the Conservatives in Mexico City and the Liberals headquartered in Veracruz. The war ended with Liberal victory, and Liberal president Benito Juárez moved his administration to Mexico City.
