After the fall of the empire, Mejía was executed on 19 June 1867, alongside Emperor Maximilian, and fellow conservative commander Miguel Miramón.

Cano was impressed by the prefect’s son, and his talent for horse riding, writing a letter of recommendation to President Anastasio Bustamante so that Mejía could be admitted to the Military Academy in Mexico City.

[4] After the United States annexed Texas, and tensions between Mexico and the U.S. were leading to war, Mejía formed part of the Army of the North sent to patrol the Mexican frontier.

[5] The American northern advance under Zachary Taylor stalled after the Battle of Buena Vista, and after the bulk of the Mexican army was called back to the capital to face Winfield Scott’s expedition from the East, Mejía was made part of a garrison that was ordered to stay in the north at San Luis Potosi where he would remain until the end of the war.

[6] In 1850 during the presidency of Mariano Arista, a revolt flared up in the Sierra Gorda led by the rebel Quiros, and Mejía was among the troops sent to pacify the region.

Mejía was made military commander of the region, but the colonization project was interrupted when the Arista administration was overthrown in 1853 and replaced by Santa Anna.

Under his administration would begin a series of reforms known as La Reforma which would include a new constitution, and among which were anti-clerical measures intended to strip the Catholic Church of its legal privileges and wealth.

Amidst nationwide conservative revolts, on 13 October, Mejía took over the town of Queretaro, proclaiming his defense of the church and also promising the Indigenous communities to protect their communal lands which had also been affected by the Ley Lerdo.

The government sent General Manuel Doblado to take back the city, and Mejía was forced to evacuate it on 21 October, heading towards the Sierra Gorda.

General Vicente Rosas Landa attempted to reach a compromise with Mejía, and offered official government recognition of his rank, an arranagment which President Comonfort opposed.

[10] The revolts against La Reforma would develop into full blown civil war after President Comonfort joined Félix María Zuloaga's Plan of Ayutla, amounting to a self coup, and which proposed to draft a new, more moderate constitution.

After taking Rio Verde's war supplies, Mejía returned to Jalpan where he joined his forces with those of Leonardo Marquez, the military head of the surviving conservative movement and Ramón Méndez to form an army of about two thousand.

[18] Mejía remained stationed at Jalpan, while Marquez went on to notable successes, managing to kill the liberal generals Santos Degollado and Leandro Valle Martínez [es].

[19] Mejía left Queretaro and the Sierra Gorda, heading towards the state of Hidalgo where on 5 July he attacked the city of Huichapan taking all of its garrison prisoner.

On 10 January, a manifesto was issued by Spanish General Juan Prim disavowing rumors that the allies had come to conquer or to impose a new government.

On 5 May 1862 Charles de Lorencez's small expeditionary force was repulsed at the Battle of Puebla, and the French army retreated to Orizaba to await reinforcements.

Like other conservatives, he did not believe that the French threatened Mexico’s independence, and by October, he openly supported the establishment of the Second Mexican Empire with Maximilian of Habsburg, as its monarch.

[25] Mejía was present at the opening of the Assembly of Notables in July, which resolved to found a monarchy and invite Maximilian of Habsburg to assume the throne.

Two days later liberal forces under Miguel Negrete attempted to take back the city only to be utterly routed, losing all of their war material and leaving nine hundred prisoners.

[29] For the second half of 1864, Mejía was stationed in the northeast of the nation working to pacify the region with Charles-Louis Du Pin and Édouard Aymard [fr].

The Republican General Negrete, with some American mercenaries, began to capture towns along the Rio Grande, and Mejía retreated to Matamoros to await reinforcements.

Imperialist forces while retaining control of Mexico City, began to consolidate at Queretaro, where the Emperor and his leading generals, including Mejía, now found themselves.