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The Failure of the Mexican-American War

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The author is a student of ancient and modern European history.


Two People, One Land

America. Once called the New World by European explorers, now separated into many different nations and cultures. Early development of the colonial empires of the New World were starkly divided between north and south, Anglo-French and Spanish, but both had a singular rule—that colonies exist to make the mother country rich.

As the Age of Enlightenment swept across the world, men began the process of realizing self-determination and threw off the shackles of colonial rule. But the states that were created in the shadow of colonialism were fundamentally different in their design and understanding of the worlds around them. These two states—both endangered by monarchal rule from abroad—could have developed close, friendly relations, but instead became bitter enemies.

The United States of America was founded on republican idealism, backed by Protestant moral codes and North European ethical identity. Capitalistic, individualistic, and anti-authoritarian, the founding documents of the USA vested political power in the American people, quite different from those of the Empire of Mexico.

While the USA was born of the idealism of English constitutionalism, Mexico was founded in the methodology of the old world. Church and State were inexorably linked together via economic and political power. Mexico was founded as an empire, and was unable to break the cycle of political change so common to old world counties. Dictators rose to fall beneath the oligarchs which led to short loved democracies that elected dictators. While the Mexican Empire was short lived, the early constitution vests authority in the army rather than the people. Having long established political structures left Mexico in a preexisting political conflict that was only to be exacerbated by American expansionism.


A Shifting Border

World events brought America and Mexico closer together. Europe’s Napoleonic Wars shattered the old regimes and debilitated the capability of the colonial powers to hold their colonies in place. Spain’s actions in the Napoleonic Wars led to social collapse, and in turn the defection of most of its colonial possessions.

Napoleón, invested heavily in European affairs and wary of British intervention, sold all of Louisiana to the United States, doubling the size of the fledgling state. Further engagement in Spanish Florida between forces of the United States Army and native Americans allied with escaped slaves led to the Adams-Onis Treaty, solidifying the border between the USA and New Spain, the Spanish territory which would become the Mexican Empire.

These constant border changes coupled with wars against the Native Americans and American settlement of the west led to various people ending up on different sides of a border drawn on a map that didn’t necessarily take into account the needs and ideas of the people it affected.

All of these combined to create the Texas Revolution. American settlers who had been invited into Texas by the Mexican government increasingly saw an authoritarian centralized Mexican state as an enemy. Revolution broke out in Texas, and after defeating the Mexican army under Santa Anna became an independent republic following the American model.

The Republic of Texas was not recognized by Mexico’s central government, an issue born of the factional politics of the Mexican state. It was however recognized and annexed by the United States of America, drastically shifting the border west and making Texas’s border problem an American border problem.

Conduct of the War

The Mexican-American War did not begin with two evenly prepared sides. Forces on both sides of the conflict were opposed to a military engagement, and yet there were those, like President Polk, who saw the Texas Revolution as an opportunity to realize Manifest Destiny and drove the nations into war.

Polk positioned American troops in positions that would spark a conflict over the disputed border and placed several pieces into place as to quickly and efficiently win the war he started. Naval and ground forces were prepared for the invasion, and by blaming the Mexicans for the war Polk called upon the patriotic spirit of the American people to volunteer for the war.

Rebels took California, while American forces marched west securing the northern portion of Mexico. Indian revolts and some uprisings from native Mexicans slowed the Americans progress, but there were few casualties and no overall defensive plan.

Marching into central Mexico was a different story. Santa Anna returned and took control of the country through deception, but was defeated by American forces. Bloody hand to hand fighting seized many Mexican cities, though the war did not see many casualties overall.

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Overall American forces quickly and efficiently seized large swathes of Mexican territory, due in part to the suddenness of the war and in part due to the factions of the Mexican governments inability to work together. Attempts to seize more Mexican territory than was taken were only stymied by partisan political action in the Senate.


The Treaty of Guadalupe Hidalgo

While the Mexican-American was ostensibly launched as a defensive measure to protect the Texan border from Mexican troops, war goals quickly shifted to fulfilling Manifest Destiny. Manifest Destiny was the idea that the American government should reach from sea to sea, encompassing the whole of North America. Military actions in California and New Mexico make it clear that the commanders put west were already preparing to annex the territory at the onset of the war.

The Treaty of Guadalupe Hidalgo was therefore a success for president Polk, at least in part. American occupation of Baja California and parts of northern Mexico hint toward a larger intended annexation. When American forces withdrew at the end of the war they brought with them collaborators who had risked their lives and lands to assist the American army. History tells us that foreign nationals will rarely help the occupier unless they think they’ll get something out of it.

If army command in north Mexico had such a plan it was dashed by the Treat of Guadalupe Hidalgo. With the the treaty the border was set at the Rio Grande and traced across to the sea in California. While the American diplomats could have gotten more from the Mexican government, as they had occupied the capital and many of the cities that were not revolting against the central government, they didn’t, because of American politics. Party and sectarian policies were placed ahead of the advancement of the nation that led to limited cessation of territory by the Mexican government.


Social Deterioration

At the end of the Mexican-American War, the political map of North America had fundamentally shifted in favor of the USA. This could be measured not simply as a matter of changing size, but in tangible goods found in the bounty of California and Texas. American settlers were free to move west with guarantees of constitutional liberty, something that the Mexican authorities had never been willing to provide.

While profoundly blessed with the lands gained in the Treaty of Guadalupe Hidalgo, America was driven into a new crisis from the acquisition of the west. Slavery reared its head, and shattered the nation's unity in the years following the victory over Mexico. Many detractors of the Mexican-American War, most notably Ulysses S. Grant, considered the Civil War to be God's punishment for the crimes committed during the Mexican-American War.

Mexico did not come out of the war much better, having lost almost half its territory while suffering through the occupation. Successive governments had collapsed, been overthrown and ultimately held hostage. Thousands had died, and families separated across a man made border when the citizens living in the ceded territory had to choose between Mexican and American citizenship. Mexico would continue to suffer serious internal trouble up until World War II.


Legacy of a Shattered Culture

Mexico’s defeat in the Mexican-American War shattered the nation psychologically comparably to other national defeats like the Mongol occupation of Russia or the English occupation of Ireland. Into the 21st century Mexico continues to vacillate from one leader to another, unable to control its own internal chaos.

America too has to deal with the fallout of absorbing a large mass of foreign citizens who were never fully assimilated and continue to have ties to an external power. Race relations in the American Southwest are a direct result of the way in which Americans seized unto Manifest Destiny and violently imposed it across North America.

Politicians on both sides of the border have, in both the immediate peace and since, used the border issue to distract citizens from issues at hand by hailing to the turbulent past. Citizens of both countries today continue to be held hostage by the failures of politicians who couldn’t look past their own election and make decisions that would benefit both states in the future.


Krauze, Enrique. "Border Battle: The Ugly Legacy of the Mexican-American War." Foreign Affairs 92, no. 6 (2013): 155-61.

Trotter, Richard L. The Arkansas Historical Quarterly 62, no. 3 (2003): 334-35. doi:10.2307/40024274.

PELLEGRINO, NICHOLAS. American Catholic Studies 126, no. 1 (2015): 73-74.

Dawson, Joseph G. The Journal of Arizona History 31, no. 4 (1990): 429-31.

© 2019 A Anders

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