Mexican-American War & St. Patrick’s Battalion, Part II

U.S. troops terrorized Mexican civilians, circa 1847. | Courtesy Library of Congress

The Mexican-American War of 1846-48 is little known today, yet it had more impact on America’s westward expansion than the opening of the California Trail or the building of the nation’s first transcontinental railroad. The conflict is often called the forgotten war, but the results were profound for the United States and Mexico.

Read Part I:  Click on History under the Explore Tahoe menu

After its military victory, the U.S. acquired two-fifths of Mexico’s territory, which became the present-day states of California, Utah, Nevada, Arizona and New Mexico. Additionally, it also encompassed parts of Texas, Colorado, Nebraska, Arkansas, Oklahoma and Wyoming. It added more land mass to the United States than all of this country’s other wars combined. The vast scale of natural resources ready for exploitation and the discovery of mineral wealth in the West added more prosperity to the national treasury than any other land acquisition.

The St. Patrick’s Battalion became an artillery force manned by primarily recently immigrated foreigners that fought directly against American soldiers.

In the 1830s and 40s, Mexico was weak and vulnerable politically and militarily due to its long colonial status under Spanish rule and its grinding 11-year War of Independence against Spain. About 600,000 Mexicans died in that fight for freedom and equality, nearly of one-tenth of the country’s population. Mexico’s revolution against Spain’s colonial authorities ended in victory in 1821, but it left the country politically unstable, with a severely weakened economy, mired in poverty and debt. By 1841, Mexico was bankrupt.

The war against Mexico was not America’s finest hour. A principle reason for the fighting was the United States’ desire to acquire the Mexican province of Alta California. Gold was not part of the equation yet, but bountiful, fertile land, Mediterranean climate zones and access to Pacific Ocean ports were. American settlers had already begun to populate the region. The 1848 American victory in the war secured California into the constellation of the United States; it became a state in 1850. President Ulysses S. Grant later wrote: “[It was] one of the most unjust wars ever waged by a stronger against a weaker nation, an instance of a republic following the bad examples of European monarchies.”



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March 23 |  Galena Creek Visitor Center, Reno | 10 a.m.
March 26 | Word After Word Bookstore, Truckee | 6:15 p.m.


After its surrender, Mexico ceded more than a half million square miles of sovereign territory. The U.S. paid $15 million for all that terrain — the same amount President Thomas Jefferson compensated French leader Napoleon Bonaparte in the 1803 Louisiana Purchase, which added a whopping 828,000 square miles of territory to the United States. Students of history know that most of the land that became the lower 48 states was acquired in quick bursts through war or negotiation. Indigenous peoples had no voice and low chances for survival in the rapid and disruptive American expansion.

The new U.S. Regular Army soldiers were paid a meager $7 per month, but the guaranteed wages combined with false promises made by recruiters attracted thousands of destitute immigrants from Europe who needed income of any kind. The young men who signed up — 25 percent were Irish — were guaranteed money, adventure, even the prospect of meeting attractive Mexican senoritas. And with a potential war looming with Great Britain over land acquisition in the Pacific Northwest, joining the army also offered the possibility of fighting against the hated British.

Forty percent of the nearly 27,000 army soldiers sent to Mexico were foreign born. Since most of them were not U.S. citizens, previous military experience did not matter. They were all inducted as privates with no eligibility for officer rank. Many Irish nationals reached America on coffin ships, escaping famine and British discrimination at home. The Regular Army troops were supplemented by more than 73,000 volunteers who served from nearly every American state. Congress had to create this volunteer class of citizen-soldiers because most state militias were prohibited from participating in military operations on foreign soil and militiamen were legally limited to 90 days of service.

Most U.S. Army troops were professional in their demeanor and conduct, with no axe to grind with Mexican non-combatants. That civility and decorum did not extend to a significant portion of the state volunteers who joined the Mexican-American War in 1846. Most were loyal only to their own state, with many of the officers sourced from the somewhat aristocratic middle and upper classes of American society. There were many volunteers from Texas and other Southern states who believed Mexicans were an inferior and degraded people. This racist attitude among some volunteer forces led to unspeakable atrocities against Mexican civilians during the U.S. military invasion and occupation. Some of the senseless cruelty was payback for Mexico’s slaughter of those Texan forces at the battles of Alamo and Goliad during the Texas Revolution a decade earlier. But much of it was just indiscriminate savagery.

The Arkansas Cavalry, known as the Rackensackers, had a reputation as a wild and calloused bunch. Convinced of their racial superiority they held “the firm belief that their own State could whip the world and Mexico in particular.” After one of their members was found killed in an ambush, the Arkansas regiment rounded up a group of Mexican peasants and in a drunken rampage proceeded to rape and kill them. Nearly 30 men, women and children were murdered.

Volunteers from the Lone Star State showed similar tendencies, indicated by the slaughter of 24 Mexicans at Rancho Guadalupe by Texas Rangers. Again, the bloodbath went unpunished as General Taylor acknowledged he had no control over these men. The Rangers, like other volunteer outfits, operated independently of Taylor’s command despite the fact that he was commander-in-chief of the entire invasion force. U. S. Army officers condemned the violent behavior, but there was little they could do to control volunteers fighting on their own volition and under their own civilian commanders.

Another result of the American aggression against Mexico is that it was the only time that U.S. troops deserted and formed their own military unit within the enemy’s army. The St. Patrick’s Battalion became an artillery force manned by primarily recently immigrated foreigners that fought directly against American soldiers. Although they were not the majority, the leadership and core of the Saint Patricios, as the Mexicans fondly called them, were Irish Catholic. Most of these men had served active duty with the British Army and were well trained in artillery and military tactics. They were disciplined and inspired to fight. The St. Patrick’s Battalion was arguably the most effective fighting machine in the Mexican Army. The leader of St. Patrick’s Battalion was Irish immigrant John Patrick Riley, a strapping, red-headed former sergeant major in the British Army.

Read Part III in the next edition or at TheTahoeWeekly.com.