May, 1846 - July, 1846
When Mexico went to war with the United States in 1846, it had more than 30,000 men under arms. In addition, individual states had their own civil militias to deal with bandits and Indian depredations. In recent years, however, the Mexican Army had proven unable to protect the far northern frontier, which had been devastated by incessant raiding by the tribes of the Southern Plains. Dominated by conservative centralists, the army had little interest in frontier defense, allocating most of its resources to divisions stationed in the interior, where they could be used by ambitious military leaders in the struggle for political power. In addition, Mexico lacked an industrial base, making it difficult for the government to outfit an army at short notice. Years of corruption and neglect had left arsenals throughout the country depleted and stocked with unreliable firearms, which Mexico had purchased from Great Britain shortly after independence.
On the eve of the war with the United States, the Herrera government sought to implement sweeping reforms to revitalize Mexico’s decaying military establishment, including the creation of a national guard. However, the reforms were opposed by the regular army. Suspicious of any efforts that might curb their power, military leaders overthrew the Herrera regime in January, 1846. (For more information, see “The Mexican Army in 1846”).