Numerous conspiracy theories center on the controversial war fought between the United States and Mexico between 1846 and 1848. One theory states that the war was a product of a conspiracy by southern U.S. congressmen to gain more southern territory, and, therefore, gain more political power.
Another view suggests that it was U.S. President James K. Polk who initiated a complex conspiracy to start a “just” war against Mexico. Yet a third theory puts the blame for starting the war on a conspiracy among an aggressive Mexican press.
As early as the Missouri Compromise (1820), the U.S. Congress had made attempts at balancing political power between the free and slave states. This balancing act continued throughout what historians call the “era of sectional conflict,” and ended only with the outbreak of the U.S. Civil War.
Abraham Lincoln was one of many politicians who saw a war with Mexico as detrimental. He and many others believed that the acquisition of southern territory would offset the balance of political power.
Both before and after the war, contemporary abolitionists, including prominent spokesmen in both the northern Democrat and Whig Parties, accused the so-called Slave Power, a suspected cabal of southern oligarchs bent on expanding slavery and the southern way of life throughout the Western Hemisphere, of arranging the war to accomplish their ends.
Though many at that time believed that President Polk was part of the Slave Power conspiracy, others then and since have pointed to Polk himself as the key conspirator in instigating the war. Polk was a prominent advocate of Manifest Destiny, the belief that it was the God-given destiny of the United States to spread from the Atlantic Ocean to the Pacific.
Mexico’s more northerly provinces— and in the minds of some, all of Mexico—were thus a legitimate target for U.S. expansion. Polk lent vocal support to this position during his campaign for the presidency, announcing his strong support for the annexation of Texas, which was currently being considered by Texas President John Tyler.
According to Anson Jones (the final president of the Republic of Texas), Polk sent agents to Texas to try to persuade him to provoke hostilities with Mexico while the annexation process was taking place, bringing the United States into a territorial war in defense of one of its states and fixing the responsibility for the war on Mexico. This suspected conspiracy, which anticipated the Mexican-American War by eleven months, did not succeed only because Jones would have no part in it.
Having failed in this conspiracy, Polk attempted the purchase of New Mexico, California, and the disputed land in Texas between the Nueces River and the Rio Grande. However, it soon became painfully clear to Polk that, after losing Texas to U.S. annexation, Mexico had no intention of parting with any more of its land.
At this point, theory holds, Polk initiated another and even more complex conspiracy by ordering General Zachary Taylor with a large army to station himself just inside the disputed territory southwest of the Nueces River. When hostilities failed to materialize, Polk ordered Taylor to the mouth of the Rio Grande, which was the southernmost fringe of the border claimed by Texas.
Once there, Taylor built a fort and blockaded the river. At the same time, a U.S. military exploring party under John C. Fremont moved into California’s Salinas Valley and Polk secretly instructed the navy to invade California should any hostilities break out between the United States and Mexico.
These actions proved sufficient to provoke Mexico. A detachment of the Mexican army defending the port city of Matamoros fought an engagement with some of Taylor’s troops, killing eleven and wounding another five. Now able to claim that Mexico had “shed American blood upon American soil,” Polk went before Congress and asked for a declaration of war.
Thus, according to this theory, a complicated conspiracy initiated by the U.S. president succeeded in starting a war. However, whether this was to accomplish his own aims or those of the Slave Power remains at issue.
Relating to this presidential conspiracy is another that points in a completely different direction. Claiming that the treaty that fixed the southern boundary of Texas at the Rio Grande had been signed under duress, Mexico repudiated both that boundary and even Texas’s right to exist as an independent republic.
Thus annexation of Texas by the United States was regarded as an invasion of Mexican sovereignty and Mexico immediately broke off all diplomatic relations. Although government and military leaders in Mexico did not want war with the United States, some have pointed to a conspiracy among the nationalistic Mexican press, which enflamed public opinion sufficiently to force a more aggressive policy.
Polk’s efforts, whether the product of a conspiracy or not, fed into the aims of this group of journalists, providing ammunition for a barrage of scathing editorials arguing that Mexico must go to war, both in retaliation for the annexation of Texas and to dissuade the U.S. from seeking to acquire more territory in the southwest. The bottom line was that Mexico’s national pride was at stake. According to this view, this culminated in the skirmish along the Rio Grande, which sparked the beginning of the war.
The Mexican-American War ended with the Treaty of Guadalupe Hidalgo (1848), which ceded nearly one-third of Mexico’s territory to the United States. In return, the United States paid Mexico $15 million and agreed to allow Mexicans living on the land to remain if they chose to do so.