The successor of Calleja, Apodaca, by his conciliatory and humane conduct, did much to tranquillize society near the capital, but ideas of independence were still working all over the country. Guerrero, who must be counted among the heroes of the movement, showed an unwearying activity in the campaign. Many times his forces were routed; many times they triumphed; neither success nor defeat made him waver. He was covered with wounds, but heeded them not; he was deaf to proposals of clemency from the royalists. In the mountains of the south, to which he retired, he kept up constant warfare upon the Spanish troops, and even set up a new national government. This he continued without falling into the hands of the royalists until 1820, when the course of Yturbide put a stop to a warfare which had lasted ten years and soaked in blood the soil of Anahuac.
The French had been driven from Spain in 1814, and Ferdinand VII. was again upon the throne, but there was a revolution in 1820, by which he was compelled to surrender much of the authority which he had taken upon himself in spite of his oaths and promises. He was obliged to convoke the Cortés, to change his ministers for liberals, to abolish the Inquisition, free the press, and re-establish the national militia.
Such events awoke again the demand for a liberal government in Mexico. It was then that an officer in the royalist army, a native Mexican, who had hitherto distinguished himself on that side, now changed his allegiance, and took up the cause of independence.
The concessions forced on King Ferdinand were celebrated in Mexico on the 31st of May, 1820, the suppression of the Inquisition and the liberty of the press being subjects of great rejoicings. The independent party saw in these reforms an opportunity to avail themselves of the new element to realize their most ardent visions. A great division was produced among the resident Spaniards of the country, for while some of these declared in favor of the constitution, the greater part showed themselves hostile to it, still clinging to ideas of absolute power, and foreseeing that so great a political change would hasten the independence of Mexico.
Agustin de Yturbide was born in the city of Valladolid, not then re-named Morelia, on the 27th of September, 1783. His parents were of native Mexican blood, Joaquin de Yturbide, born in Pamplona, and Ana Arámburu.
He had entered a royalist regiment before he was sixteen years old, and until 1808 he showed himself a vigorous opponent of the liberal party, serving with his troops in different parts of the country, always signalizing himself by his valor, his activity, and his adroit combinations to bring about the defeat of the cause opposed to his own. Through the intervening grades he passed to be colonel, and held commands of importance at Guanajuato and Valladolid.
In the diversity of opinions of 1820, Yturbide was among those who accepted the idea of a complete separation for Mexico from the Peninsula. Just at that time the viceroy conferred upon him the grade of brigadier, and gave him command of a body of troops destined to operate against the insurgents of Guerrero in the south.
Yturbide left the capital in November, and a month later found himself confronted by an enemy of something like three thousand men. After several encounters unfavorable to his command, Yturbide entered into an active correspondence with the opposing chief, the result of which was an interview for friendly conference. Both generals found themselves in accord, for, to the surprise of Guerrero, his opponent revealed an ardent desire to proclaim independence. Guerrero, without personal ambition, willingly handed over the command to the renegade, who announced, on February 24th, the so-called "Plan of Iguala."
Three essential articles made up this proposal: (1) the preservation of the Roman Catholic Church, with the exclusion of other forms of religion; (2) the absolute independence of Mexico under the government of a moderate monarchy with some member of the reigning house of Spain upon the throne; and (3) the amicable union of Spaniards and Mexicans. These three clauses were called the "three guaranties." When the national Mexican flag was devised later, its colors represented these three articles of the national faith—white for religious purity, green for union, and red for independence. The army of Yturbide was known as the army of the three guaranties.