In December 1822 Antonio López de Santa Anna and General Guadalupe Victoria signed the Plan de Casa Mata, a pact through which they sought to abolish the monarchy and transform Mexico into a republic. Initially a supporter of Iturbide, Santa Anna had adopted the republican cause. Agustín I was forced to abdicate and left the country. In May 1823, following Iturbide's resignation, Victoria became the first president of Mexico and Santa Anna became governor of Yucatán. Yucatán joined as the Federated Republic of Yucatán on December 23, 1823. Both were founding states of the United Mexican States.