Why the United States Did Not Annex Mexico after the Mexican-American War

The Mexican-American War (1846-1848) has unfortunately slipped into the category of America’s “forgotten wars”. Its relative brevity, close proximity to the American Civil War, and relatively minimal long-term effects have led it to evaporate out of the minds of most Americans.

Indeed, the average person could not tell you a single thing about the conflict, save perhaps that we obtained much of the American southwest as a result of it. That large land acquisition however is exceptionally important, as it was the primary reason for the United States provoking the conflict. What is interesting however is that despite our total victory over Mexico in 1848, the U.S. government stuck to its original land requests of 1845 and nothing more. We did not attempt to annex Mexico as a whole, as total conquerors normally have done. As American troops occupied Mexico City, the Mexican government had little bargaining power to resist such a demand had we made it.

The question however is why we failed do so, and the answer is we simply didn’t want to, for various reasons. In the era of ongoing problems with Mexico over illegal immigration, this essay will explain why the United States proved to be a fair-minded victor by only seeking its original land claims, paying for it, forgiving debts, and allowing Mexico to retain its sovereignty.


After the Mexican War, many elements in the United States opposed annexation of the entire nation for various reasons, but among the major reasons, racism was the pivotal factor. Mexico was a nation of six million ethnically mixed people who were of Spanish, African and Native American origin, respectively.

Needless to say, there was a significant amount of racial blending from the days of colonialism, thus the Mexican population was anything but single-blood. There was a significant caste system which existed in New Spain (Mexico) prior to independence that enforced many racial classifications, but after independence from Spain in 1821, such classifications largely were disregarded. Nonetheless, Mexico remained quite racially diverse with large amounts of brown and dark-skinned individuals. Similarly, the population of Mexico is and was overwhelmingly Roman Catholic. In that era, before the large-scale influence of Protestantism, the Catholic Church held a very tight grip on the country’s people and practices. In fact, it was the only religion permitted in the country under its 1824 Constitution. They would not have been inclined to try something new, even with the liberty to do so. Lastly, slavery had been abolished entirely by 1829 and by 1848 the last vestiges of it were long eradicated.

By contrast, the United States of America in 1848 had a population of roughly twenty-one million people. Some fourteen million of them were white, mostly Protestant, and had Anglo-Saxon ancestry with traces of Irish, German, French, and other western European roots. Additionally, three million of these people were African-American, two million of which were enslaved and roughly one million which were free. The Native American population was not accurately documented during this time, but their numbers were still arguably 2-3 million. Next, American culture in this era had a very deep canyon of inequalities between whites and non-whites of all groups. Most African-Americans were enslaved and those who were free were still subject to various types of discrimination regardless of the states where they resided. Native Americans, while not enslaved, still were being actively persecuted as well with the constant loss of their ancient lands and forced relocation westward. Lastly, Roman Catholics in the United States although legally free to practice their faith, were still shunned a great deal by many in society.

Catholics were still viewed with great suspicion by the mainstream Protestant majority and often faced legal discrimination in employment, accommodations, and housing. Therefore, those who made the racial argument against annexing Mexico feared adding six million brown, black, mestizo, Roman Catholic and Latino persons to the American fabric. In their minds, it would be next to impossible to assimilate these individuals into the majority white Protestant culture. Similarly, as Mexico was a “free society” where slavery had been abolished by law for more than two decades, it would be unthinkable to presume that anyone there would resubmit to conditions of servitude, having been free for so long. All Mexicans would likely demand equal treatment with whites in the United States and that perhaps would have been a bit radical of a proposition in 1848.

Therefore, based on the aforesaid evidence, racial and religious harmony was not likely and annexation with Mexico was simply an unthinkable proposition.


Another powerful argument against the annexation of Mexico was that against the perceived imperialism of such a move. Manifest Destiny, the belief system that this republic had the inherent right to expand across the continent without infringement, had already guided the United States to the Pacific Ocean with the Oregon territory. These previous acquisitions however had been done through treaties and purchases. Never before had such a large land acquisition been obtained through war, and we had certainly not ever conquered another country in the name of expansion. The thought of that very move troubled many Americans for the following reasons.

First, we ourselves had been colonial subjects from 1607-1776 and morally, having been colonies, should avoid at all costs making colonial subjects of others. Next, to assume such a role would place the United States on the level as Great Britain, our mother country and chief diplomatic rival in the world. While Americans had an affinity for British people and culture, British territorial and economic objectives were often at odds with those of the United States. The two nations, while very close today, were essentially “friendly enemies” in the 19th century that viewed one another with suspicion and cautiousness. In sum, we did not wish to emulate British governmental objectives and its desire for worldwide empire, at least at this time. That would come somewhat later in the future. For now, our focus was on North America, and even then, it didn’t include the destruction of sovereignty for any other country. Lastly, for the United States to even think about annexing Mexico would have gone against the pure spirit and essence of the Monroe Doctrine- at least to Europe. That doctrine, issued by President James Monroe in December 1823, held that North and South America were officially “off limits for further European colonization”.

While the purpose of the doctrine was both to scare off Europe from re-colonizing anywhere in the Americas and to theoretically support the independence of the new countries in Latin America, it had hidden motives. President Monroe’s real motive was not to preserve the sovereignty of our neighbors, but rather to prevent European colonization of any areas of commercial and strategic interest to the United States. We therefore wanted to reserve for a later date our possible attempt at economic and or commercial colonization of Latin America, without European interference. Nonetheless, Great Britain, France, and Spain saw the Monroe Doctrine as a clear blanket against them moving against any further territory in the Americas, and an implicit pledge by the United States to not move against the new countries in any way either. We were the nation who would go to war to preserve the freedom of these countries.

For the Monroe Doctrine to remain a true force, the United States had to keep up appearances that it too was not interested in exploitation and annexation of anywhere in Latin America. Everything we did would have to be somewhat discreet. Because that image would be threatened by any other means, the United States had to backhand instigate the war with Mexico. If they were seen as the aggressor, we would be merely defending ourselves. Therefore, to take a large chunk of Mexico’s land was not appealing to many of those at home and abroad, but it was the lesser of two evils in comparison to complete annexation. That in turn would have been tantamount to colonization and exploitation. Many Americans were not willing to go down this road, and thus total annexation of Mexico simply was not an option. Not only would it have likely provoked outrage from Europe, but also a serious rebuke on the domestic policy front as well.


The next reason the United States declined to annex all of Mexico was because we entered the conflict with very specific territorial ambitions. Those designs never once included the annexation of the whole country, but just certain parts. Specifically, well before the war started, the United States, so hungry for ocean to ocean expansion, offered to pay Mexico twenty-five million dollars for the following tracts of territory, the Texas border down to the Rio Grande, Alto California and Santa Fe Nuevo Mexico. These lands cover the modern-day states of Texas, Oklahoma, California, Nevada, Utah, Colorado, Arizona, and New Mexico. Not only were these lands very sparsely populated, but they were very rich in resources.

The primary goals of the United States in wanting these lands were to prevent British, French, and potentially Russian expansion in the area and to have a working port on the Pacific Ocean. The whole package included a forgiveness offer of 3 million for damages owed to American citizens from Mexico’s War of Independence from Spain, plus the above 25-30 million for the lands sought. Mexico’s instability in this era effectively preempted the nation from being able to negotiate this offer from the United States. Even if stability were present, most Mexican authorities opposed selling any of their country to the United States in the name of national honour. When Mexico seemed unwilling to take the bait, the United States began a series of provocative diplomatic and military moves to lure Mexico into war. In truth, we did not seek a war with Mexico if able to obtain these lands peacefully, but as they did not reciprocate, we changed our course of strategy.

Even with this change, American political and military commanders never sought or considered the annexation of the entire Mexican nation at any point. Simply put, much of the lands we sought were sparsely populated (which aids the racism reason) and had fertile regions for farming and commercial development. Similarly, the topography is very mountainous with deserts and plateaus. Aside from the people who lived in these areas not being wanted, the United States likely did not view much of what was then central and southern Mexico to be of any material value for American enrichment. Our land claims were very specific, and they were all in the far northern part of the country closest to the United States.


Lastly, upon the conclusion of the Mexican War, the United States was very practical and reasonable with its demands to Mexico. Despite the fact that they were completely conquered, to the point of having their national capital occupied, the United States did not view itself as a conqueror. We kept the land claims to what we had originally requested in 1845, still paid Mexico 15 million for the territory, and assumed 3.25 million in debts that Mexico owed the United States.

Why did we still pay Mexico and forgive debts? The reason lies in the fact that we did not want to be viewed as conquerors, either at home or abroad. The United States knew that even in defeat, the Mexican nation was still very viable and nationalistic, which leads to the other half of this story. American political and military leaders were likely well aware of that nationalistic spirit within Mexico. Even if they were interested in full annexation of the country, they likely knew that attempting to either subdue or assimilate its people into American society would be a fool’s mission. Mexicans were exceptionally proud of their nation, culture, and would not take well to being “Americanized” in any way. Additionally, Mexico was and is a large country with very diverse geography.

To even come close to successfully occupying Mexico would have required a significant long term financial and military commitment from the United States. Undoubtedly, this would have taken many resources away from much more needed endeavors. Even if those two bases were covered, the sheer amount of underground resistance to American occupation both in the cities and the countryside that would likely occur, cannot be underestimated. Our forces would constantly be threatened and subjected to attacks daily. Similarly, higher taxes would have been needed to pay for a much larger army. Eventually, the American public would have demanded that forces be withdrawn, much like in Iraq in our times. Thus, annexation of Mexico would have been a political and military disaster for the United States very early on.

Arguably, had annexation taken place in 1848, the Americans wouldn’t have had the means or desire to attempt subjugation of the Mexican people beyond 1858. Mexico would have had its sovereignty restored before the U.S. Civil War, and hopefully a more stable government would have been born as a result of American governance. While the previous statement is debatable, what is certain is that had we demanded annexation, the United States would not have been able to hold Mexico for any longterm period. Occupation would prove much too costly in multiple ways, with very little to show for it.


To summarize my points, the United States of America had no interest whatsoever in annexing Mexico in 1848. Our reasons were racial, anti-imperialist, land claim specific, and practical. The goal of the United States was not to conquer another country, but to simply add to its territory, expand westward (primarily) and fulfill the goal of manifest destiny. American policymakers likely had the foresight to know that the price of Mexican annexation was too great to bear for the nation. Indeed, there would have been severe consequences both internationally and domestically. Wisely however, we chose to stick to the original game plan.


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