Expeditionary Land Power

Lessons from the Mexican-American War

Maj. Nathan A. Jennings, U.S. Army

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By June 2015, morning battlefield-update briefs were routine in the 3rd Brigade Combat Team (BCT) of the 82nd Airborne Division’s Baghdad command post. On one morning of that month, however, there was a critical difference: it was the first time a member of the staff was asked to provide commentary and analysis about the politics-and-policy decisions of regional governments, coalition partners, and the government of Iraq. Given my position as an assistant professor of American politics, policy, and strategy at the United States Military Academy at West Point, Col. Curtis Buzzard, the 3rd BCT commander, asked me to help explain how the 7 June national elections in Turkey might influence our partnership with the Iraqi Army’s Ninewa Operations Command and the operational planning to liberate Mosul.

Since drawing down its large-scale counterinsurgency campaigns in the Middle East, the U.S. Army has been increasingly adopting, as described by its thirty-eighth chief of staff, “an expeditionary mindset” to “conduct forced entry in denied areas under extremely austere conditions anywhere in the world.”1 While many are turning to the two world wars and interventions in Korea, Vietnam, Afghanistan, and Iraq for applicable lessons, the campaigns of the nineteenth century—with the exception of the Civil War—may offer more relevant case studies where relatively small, technologically advanced, and professionally led forces deployed to distant theaters. From the Indian Wars that raged across expanding American frontiers to the global attacks of the Spanish-American War, the republic’s oldest military service evolved to negotiate rapid and economized expeditionary warfare in both conventional and guerrilla settings.2


In the Mexican-American War, 1846–1848, a series of sparsely resourced but highly effective expeditions exemplified the U.S. Army Operating Concept’s imperative for future forces to jointly “present the enemy with multiple dilemmas” by being able to “conduct expeditionary maneuver through rapid deployment and transition to operations,” and “overwhelm the enemy physically and psychologically.”3 Beginning with border skirmishes along the Rio Grande and ending with the occupation of half of Mexico from San Diego to Veracruz, the Army, in concert with the Marine Corps, the Navy, and the diplomatic corps, employed unprecedented joint unity of effort, robust “total force” cooperation between professionals and volunteers, and relatively sophisticated foreign governance policies to achieve strategic objectives. Although the casus belli remains controversial, the efficient implementation of joint force effort across the continent established the United States as the dominant nation in North America.

Future U.S. forces will need to achieve mastery of force projection methods reminiscent of successful operations in the contested cities of Los Angeles in 1846 and Mexico City in 1847, while incorporating twenty-first century technologies to project land power effectively. While the modern U.S. military could potentially replicate massive mobilizations similar to the Second World War or the substantial deployment of the Persian Gulf War in the near future, it is more likely to conduct forced entry and security efforts along accelerated political timelines with limited but tactically effective joint and combined arms teams.

Campaigning in Mexico

The Mexican-American War and its relevance to the Army’s current interests in the Middle East, Eastern Europe, and East Asia can be readily assessed according to modern U.S. military doctrine. The operational phases of shape, deter, seize initiative, dominate, stabilize, and enable civil authority, as outlined in Joint Publication 3-0, Joint Operations, provide a ready conceptual framework to contextualize the nineteenth-century confrontation.4 While all historical engagements must be assessed as unique events within distinct panoramas, the sequenced invasions and occupations of north, west, and central Mexico by land and sea followed a campaign pattern similar to phased models that regionally aligned forces may potentially apply during forced-entry operations in the twenty-first century.

The first, and enduring, phase of U.S. military operations abroad centers on shaping the security environment. According to joint doctrine, aligned forces conduct continuous missions, tasks, and actions to dissuade or deter adversaries and assure friends while “influencing adversaries’ and allies’ behavior.”5 These efforts often focus on robust security cooperation by partnered elements to reinforce and enable political objectives. As seen in Europe, the Persian Gulf region, and the Korean Peninsula since the rise of American global leadership, expeditionary operations by combined arms teams remain a primary instrument for influencing foreign affairs in accordance with national interests.

For decades before the Mexican-American War, the Army shaped the North American security environment by operating in dispersed contingents as it secured frontiers and coastlines against both tribal and nation-state competitors. Similar to contemporary deployments by regionally aligned detachments, America’s mid-nineteenth-century ground formations rarely united for large-scale training maneuvers or campaigns. Instead, under constant fiscal constraints, they focused on economized security efforts that, contrary to popular belief, often included partnership with Amerindians and territorial militias.6

When shaping operations prove insufficient, joint forces conduct intensified posturing and maneuver to “deter an adversary” through demonstration of “friendly capabilities and the will to use them.”7 The current positioning of rotational American and allied brigades in eastern Europe and South Korea, for example, underscores how military deterrence through physical presence remains viable in the twenty-first century. While effective messaging can emanate from a variety of instruments of national power, ground forces often provide the most credible demonstrations of national resolve. As argued by Lt. Gen. H. R. McMaster, “forward deterrence involves land forces. ... It is very difficult to achieve political outcomes from standoff range.”8

When Mexico threatened war over American annexation of its former territory, Texas, scattered U.S. Army garrisons coalesced to deter potential incursion across the Rio Grande. In January 1846, in response to a Mexican Army buildup along the border, Brig. Gen. Zachary Taylor led the newly formed “Army of Observation,” comprising approximately 3,900 infantrymen, artillerymen, and dragoons, to the Gulf Coast.9 Similar to the massing of allied forces in West Germany in the 1950s to deter Russian aggression, Taylor aimed to dissuade Mexico from challenging U.S. territorial claims through physical presence. Also similar to today, the ad hoc army benefited from a degree of professionalization that allowed the regiments to join, if imperfectly, as a combined arms team.

Because of the regular army’s strength at fewer than 7,500 soldiers at the onset of war, the United States was compelled to adopt a mobilization model similar to what it uses today: heavy reliance on volunteer units to conduct “total force” campaigns of mass and scale.10 When Taylor established camp at Corpus Christi, he received, integrated, and trained state regiments from Ohio, Kentucky, Tennessee, Mississippi, and Texas to create the “Army of Occupation” in the contested territory. Throughout the next two years, thousands of volunteers from nearly every state would rotate to provide the combat power necessary to defeat the far larger Mexican military. Though use of volunteers often came at a heavy price due to their indiscipline, many recruits, such as western frontiersmen who specialized in irregular tactics, added special capabilities to the regulars’ conventional strengths.11

The third phase of joint operations begins when deterrence fails and decisive action is required. When conflict becomes unavoidable, American forces transition from posturing to seizing operational initiative. According to Army Doctrine Reference Publication 3-0, Unified Land Operations, this foundational action is designed to “gain a position of advantage that degrades and defeats the enemy throughout the depth of an organization.”12 As proven in the Inchon Landings of the Korean War and the sweeping envelopments of the Persian Gulf War, unified teams that attack rapidly and forcefully at the onset of hostilities or at advantageous points during major combat operations can dictate the battle and exploit opportunities.

For Taylor and his small army, deterrence soon failed and both sides moved to seize initiative. The American main force quickly won bloody victories at Palo Alto and Resaca de la Palma along the Rio Grande in May 1846. These victories allowed invasion of northeast Mexico while smaller columns conducted deep attacks into New Mexico and California. Though small in size, each of the expeditions employed technological overmatch to defeat an array of defending Mexican garrisons—except for a tactical setback near San Diego.13 Akin to numerous twentieth-century campaigns where operational initiative compensated for inferior numbers, rapid successes allowed American troops to occupy favorable political terrain and ultimately empowered the U.S. government to demand strategic concessions.

The economized forced entry into Alta California, in particular, reflected a high degree of joint cooperation between Army forces, the Navy’s Pacific Squadron, and rebel militia as they defeated and expelled the Presidio garrisons. When an element of the 1st U.S. Dragoons under Brig. Gen. Stephen Kearny initially suffered defeat at the Battle of San Pasqual in December 1846, a coastal contingent of marines and sailors reinforced the horsemen to win several follow-on engagements, retake Los Angeles, and establish a provisional government. Though the partnership was marred by interservice rivalry, the joint success accelerated American gains. Two thousand miles to the east, the Navy’s Home Squadron likewise blockaded enemy ports across the Gulf of Mexico while protecting logistical transports in support of Taylor’s capture of Monterrey.14


The dominate phase of an operation, according to joint doctrine, “focuses on breaking the enemy’s will to resist” or on “control [of] the operational environment.”15 Usually reflecting the most destructive moments in expeditionary warfare, Army formations dominate their adversaries through both traditional military means and emerging technological offsets. The phase often culminates a successful campaign—sometimes deceptively so, as seen in the American invasion of Iraq in 2003—by shattering the opposing nation’s military and economic capability to resist and allowing advancing forces to control politically important spaces.

In the Mexican-American War, the American culmination occurred when Winfield Scott, commanding general of the U.S. Army, led an audacious amphibious attack into Central Mexico via the Atlantic Coast (figure 1). Similar to when a modestly sized and technologically advanced coalition rapidly attacked in Afghanistan in 2001, the Army relied on operational mobility and combined arms superiority to accomplish the contested entry. Outnumbered and far from support, Scott’s eleven thousand soldiers captured the port of Veracruz and marched inland along increasingly vulnerable lines of communication to defeat over thirty thousand defenders and capture Mexico City. Arthur Wellesley, 1st Duke of Wellington, renowned for his 1815 victory at the Battle of Waterloo, reportedly called the invasion “unsurpassed in military annals.”16

As with previous successes in northern Mexico, the littoral attack relied upon cooperation by diverse military elements. In the largest wartime collaboration between U.S. ground and naval forces to that point in American history, the Home Squadron transported Scott’s entire invasion force to the coastal fortress of Veracruz, blockaded the city, and provided heavy cannon to allow an intensive eighty-eight-hour bombardment. Following the “Gibraltar of Mexico’s” timely capitulation, U.S. Marines then marched with the Army brigades “to the halls of Montezuma” while fighting in nearly every battle. Throughout the domination of Central Mexico, just as had occurred under Taylor, thousands of volunteers fought alongside regulars while warships secured maritime lines back to supply depots in New Orleans (figure 2, page 46).17

The fifth, and sometimes most challenging, phase of expeditionary warfare is stabilizing the theater after the end of major combat operations. Intended to “restore local political, economic, and infrastructure stability,” American joint forces conducting stabilization have remained in numerous countries, sometimes indefinitely, as exemplified by postwar military partnerships with Germany and Japan, after winning large-scale confrontations.18 In other situations, U.S. elements have completely departed with disastrous results—perhaps best illustrated by Vietnam—or retrograded and then returned to stabilize, as is currently occurring in Iraq. Regardless of residual intensity, American incursions often evolve into partnerships with allied governments in order to create desired strategic conditions.


The Army’s mandate to occupy and govern Latin America’s most populous country proved just as difficult in the nineteenth century as similar efforts would centuries later in places like Indochina and Mesopotamia. Frustrated American garrisons pacified restive urban centers from Sacramento to Veracruz while countering a determined “Guerrilla Corps” formed to, as proclaimed by one Mexican general, “attack and destroy the Yankee’s invading army in every way imaginable.”19 Only by implementing stability policies that ordered civilians left unharmed, quartermasters to purchase provisions locally, demonstration of respect for Catholic traditions, and partnership with Hispanic constabularies, did the occupiers prevent a popular uprising. In the end, despite numerous violations by ill-disciplined soldiers, Scott’s relatively sophisticated approach, in addition to rising internal conflict among Mexican factions, allowed him to “conquer a peace.”20

Scott’s occupation of central Mexico, and to a lesser extent, Taylor’s occupation of Monterrey, featured critically needed integration of the specialized skills that both regulars and volunteers contributed to the combined force. The commanding general employed a disciplined professional infantry to occupy the urban centers and to train allied Hispanic soldiers. He unleashed federalized Texas Rangers—irregular cavalry who had fought Mexicans and Indians for decades along embattled frontiers—to suppress the implacable guerrillas that preyed on convoys and outposts. Despite their tactical effectiveness, the Rangers’ brutality toward Hispanic civilians threatened to undermine the expedition’s broader pacification efforts.21

The final phase of expeditionary warfare enables a civil authority to “regain its ability to govern and administer to the services and other needs of the population.”22 As seen in recent operations in the Middle East, ideal transition conditions can be difficult to achieve. They sometimes require reengagement of forces. Identifying and empowering legitimate indigenous governing institutions can also be complicated by social and ethnic fracturing common in war-torn countries. In the end, expeditionary forces usually attain a manageable political outcome—as opposed to a perfect one—in order to allow redeployment of combat power from the occupied territory.


Despite its precarious position at the close of the Mexican-American War, the Army’s threat to occupy northern Mexico indefinitely, with enduring naval support, enabled diplomatic counterparts to negotiate strategic concessions in exchange for a peaceful withdrawal.

The United States paid $15 million for 529,000 square miles across parts of what is now New Mexico, Arizona, Nevada, Colorado, Utah, and California, while solidifying control of Texas.23 Mexico, under foreign rule and suffering massive peasant revolts in the Yucatan region, bitterly conceded the territory to regain sovereignty. The American garrisons then redeployed to once again secure newly expanded frontiers. Though the settlement reflected aggrandizement that the international community now would consider unacceptable, the phased campaign set precedence for similar force projection cycles—some successful and some not—throughout succeeding centuries.

Given the strategic success of the American expeditions that fought through adversity and uncertainty in Mexico, the underappreciated conflict holds opportunity for further study as heirs to the legacy of nineteenth-century forces train to “win in a complex world.” While the Civil War and the Second World War typically garner the attention of historians, they reflect mobilization paradigms the United States is unlikely to soon experience. Later interventions in Korea and Vietnam, though less vast, likewise reflected far larger investments than recent campaigns in Mesopotamia and South Asia enjoyed. Though no future is certain, these trends suggest that the Army—now smaller than at any time since 1940—will accomplish future forced entries under substantial resource constraints with increasing reliance on joint cooperation.24

This circumstance imparts new relevance to the Mexican-American War. Beyond decisive victories at storied places like Buena Vista, Cerro Gordo, and Chapultepec, the Army’s ability to collaborate with maritime partners, integrate volunteer contingents into a “total force” concept, and apply balanced governance policies in occupied territories led to the efficient attainment of most national objectives. These mutually reinforcing tactical, operational, and strategic efforts, especially when contrasted against recent suboptimal outcomes in Iraq and Afghanistan, reveal a time when commanders successfully planned and directed, as now required by joint doctrine, the “deployment of forces and the arrangement of operations to achieve operational and strategic objectives.”25

Looking forward to a new century of campaigns, the implications of the United States’ historic victory in the Mexican-American War are clear: its land power institution must train and equip to win across all the phases of expeditionary warfare as it deploys to seize initiative, dominate the enemy, and stabilize war-torn regions. Accomplishing these tasks, which fulfills the Operating Concept’s requirement to “deter adversaries; respond rapidly to crises; and conduct expeditionary maneuver against enemy forces,” will require seamless unity of effort between diverse elements of U.S. national power.26 If the war against Mexico demonstrated the potential for the Army to lead multifaceted teams to decisively win on distant and unfamiliar terrain, future endeavors in far-flung theaters will surely provide the opportunity, and ultimate crucible, to do so once again.


  1. Patrick J. Murphy and Mark A. Milley, A Statement on the Posture of the United States Army 2016, presented to the 114th Congress, 2nd sess. (Washington, DC: Department of the Army, March-April 2016), accessed 10 November 2016, https://www.army.mil/e2/rv5_downloads/aps/aps_2016.pdf; “2015 Index of U.S. Military Strength,” The Heritage Foundation website, accessed 8 November 2016, http://index.heritage.org/military/2015/; Dan Parsons, “Odierno Calls For Expeditionary Army After Afghanistan,” National Defense (blog), 22 October 2013, accessed 8 November 2016, http://www.nationaldefensemagazine.org/blog/Lists/Posts/Post.aspx?ID=1310.
  2. <2. Allan R. Millett and Peter Maslowski, For the Common Defense: A Military History of the United States of America from 1607–2012, 2nd ed. (New York: The Free Press, 1994), 127–28.
  3. U.S. Army Training and Doctrine Command (TRADOC) Pamphlet (TP) 525-3-1, The U.S. Army Operating Concept: Win in a Complex World (Fort Eustis, VA: TRADOC, October 2014), iii.
  4. Joint Publication (JP) 3-0, Joint Operations (Washington, DC: U.S. Government Publishing Office [GPO], 11 August 2011), V-6.
  5. Ibid., V-8.
  6. Millett and Maslowski, For the Common Defense, 123.
  7. JP 3-0, Joint Operations, V-8.
  8. H. R. McMaster, quoted in Tara Copp, “Army General: Land Forces Could Have Stopped Russia,” Washington Examiner website, 19 February 2015, accessed 8 November 2016, http://www.washingtonexaminer.com/article/2560424.
  9. William DePalo, The Mexican National Army, 1822–1852 (College Station: Texas A&M University Press, 1997), 97–98.
  10. Steven A. Carney, The U.S. Army Campaigns of the Mexican War: Guns Along the Rio Grande: Palo Alto and Resaca de la Palma (Washington, DC: U.S. Army Center for Military History, 2005), 7, 11.
  11. K. Jack Bauer, The Mexican War, 1846-1848 (Lincoln, NE: University of Nebraska Press, 1974), 72.
  12. Army Doctrine Reference Publication 3-0, Unified Land Operations (Washington, DC: U.S. GPO, 16 May 2012), 2-1.
  13. Bauer, The Mexican War, 59–62, 188–89.
  14. Ibid., 108, 188, 190–92.
  15. JP 3-0, Joint Operations, V-8.
  16. Arthur Wellesley, 1st Duke of Wellington, quoted in Arthur Howden Smith, Old Fuss and Feathers: The Life and Exploits of Lieutenant General Winfield Scott (New York: Greystone Press, 1937), 250.
  17. Timothy Johnson, A Gallant Little Army: The Mexico City Campaign (Lawrence, KS: University Press of Kansas, 2007), 11, 49.
  18. JP 3-0, Joint Operations, V-9.
  19. Jacob Oswandel, Notes of the Mexican War, 1846-1848, eds. Timothy Johnson and Nathaniel Hughes (Knoxville, TN: University of Tennessee Press, 2010), 78.
  20. Johnson, A Gallant Little Army, 252–53.
  21. Ibid.
  22. JP 3-0, Joint Operations, V-9.
  23. Johnson, A Gallant Little Army, 268.
  24. Jim Tice, “Army Shrinks to Smallest Level Since Before World War II,” Army Times website, 7 May 2016, accessed 8 November 2016, https://www.armytimes.com/story/military/careers/army/2016/05/07/army-shrinks-smallest-level-since-before-world-war-ii/83875962/.
  25. JP 3-0, Joint Operations, I-13.
  26. TP 525-3-1, The U.S. Army Operating Concept, 17.

Maj. Nathan Jennings, U.S. Army, is a student in the School of Advanced Military Studies, Fort Leavenworth, Kansas. His previous assignments include assistant professor of history at the U.S. Military Academy, headquarters troop commander and cavalry troop commander in the 1st Cavalry Division, security force platoon leader in the 1st Infantry Division, and cavalry scout in the 2nd Armored Cavalry Regiment (light) with Operation Iraqi Freedom tours in Baghdad and Kirkuk. Jennings earned an MA in American history from the University of Texas at Austin. He is the author of Riding for the Lone Star: Frontier Cavalry and the Texas Way of War, 1822–1865

January-February 2017