Consequences of the Mexican War

Part the last of our series on interesting facets of the Mexican War concludes with the 1848 peace Treaty of Guadalupe Hidalgo, which gave the United States full ownership of Texas, with its western border at the Rio Grande, and the modern States of California, Nevada, Utah, New Mexico, almost all of Arizona, Colorado, and part of Oklahoma, Kansas, and Wyoming (the rest of Arizona and New Mexico would be acquired through the 1853 Gadsden Purchase). In return, Mexico received a little over $18 million in compensation and forgiveness of $3.25 million owed by Mexico to the U.S.

Immense as the territories ceded by Mexico were, there were a number of U.S. Senators who urged Congress to take advantage of Mexico’s internal political chaos and force it to also give up its states of Nuevo León, Coahuila, and Tamaulipas, in today’s northeastern Mexico. This would have extended the U.S. hundreds of miles beyond Texas’ current southern border. Partly because there was growing opposition to the war in the U.S. (Illinois Rep. Abraham Lincoln was opposed), and partly because the parts of Mexico that the U.S. had so long desired, particularly California, were already handed over, Congress declined to pursue the war any longer, and this plan was dropped.

The Mexican Cession was at once a great acquisition for the U.S. and the end of the U.S. as it had been. The new lands made the slavery debate impossible to resolve through political compromise. The 1820 Missouri Compromise would have allowed slavery in New Mexico, Arizona, and the southern half of California, but not in Colorado, Utah, Kansas, or Wyoming. But anti-slavery Americans were not about to let California, the greatest prize of them all, the one that held out the most promise to small farmers and free labor, become a slave state (since a state could not be half-free, half-slave, California ran the risk of becoming a full slave state). Pro-slavery Americans knew that New Mexico and Arizona were not lands that lent themselves to plantation farming, and determined more fiercely than ever to have California, and the farmland that would become Kansas, too.

Free-Soil, free-labor, anti-slavery, and abolitionist Americans said now was the time to contain slavery altogether—to see the new territories not in the context of the north-south line of the Missouri Compromise, but as The West, a new entity that was not bound by the north-south politics or agreements of the eastern states. Keep slavery out of The West, they said, and keep it contained in the southern states until slave states were so outnumbered by free states, and slavery such an anomaly in the country, that slavery itself would die out.

Pro-slavery Americans had been ready for this fight for years. The nation had expanded along the Missouri Compromise line for nearly 30 years, it was the law of the land, there was no reason to change it, and any anti-slavery agitation in The West would be illegal, and punishable by law.

The problems the Mexican Cession caused would have to be quickly hammered out in the Compromise of 1850, a five-part piece of legislation that tried to create true compromise between anti- and pro-slavery Americans, not along purely geographical lines, but more philosophically. Slavery was not banned in the West (1), but California would enter the Union as a free state, end of story (2). Each of the remaining  western territories that wanted to become a state would decide on its own whether to come in as slave or free: popular sovereignty let the people in the territory vote on their status before applying for statehood (3). The Fugitive Slave Act was introduced, which allowed slaveholders to violate the personal liberty laws in free states (4), and slavery would remain a feature in the capital, Washington, DC (5).

This Compromise would be short-lived. As settlers poured into all regions of the Cession, the stakes became higher and higher on both sides of the slavery issue. Pro-slavery Americans needed numbers; they couldn’t allow slavery to be restricted to the existing southern states or their needs would never be met in Congress, where free-state Representatives and Senators would far outnumber slave. Anti-slavery Americans also needed numbers, to reduce slavery to a regional curiosity of a small number of states, rendered economically useless. The battles over how western states would come into the Union led to vote-rigging, where people from outside a territory would pour in when it came time to vote slave or free, making a mockery of the concept of popular sovereignty. The violence that ensued in these situations was made legendary in Bloody Kansas.

In short, the Mexican War was most important both for expanding the U.S. and for hastening the coming of the Civil War. Both events made the nation greater, one geographically, one morally. It was a dress-rehearsal for the Civil War in that so many men who fought together in the Mexican War fought against each other in the Civil War, including both Ulysses Grant and Robert E. Lee. And it nearly completed the U.S. conquest of the continent between Canada and what was left of Mexico (the last bits settled in the Gadsden Purchase). The discovery of gold in California the year after the war ended spurred not only Californian settlement but the western rush of pioneers that dominated American demographics until the end of the 19th century. It also left the United States as the undisputed great power of the western hemisphere—a great deal of impact for a war that is often skipped over as students of U.S. history move from the Revolutionary War directly to the Civil War.

California, Californios, and Americans

Part 4 of our series on interesting aspects of the Mexican-American War takes us to California. California is part of the Mexican War, of course, because what is now the State of California was northern Mexico at that time. While many Easterners in the U.S. talked almost mystically of the riches of California, and how it was the fairest land on the continent, the distance and the fact that it was a foreign country kept the number of U.S. settlers in Upper California very small.

John C. Frémont was an American who wanted to annex California, and hoped to do so almost single-handedly. He had been granted permission by the U.S. government to explore in the west, and was supposed to be canvassing the Disputed Area (now Oregon and Washington) in December 1845, but Frémont took his time moving through northern Mexico, dragging his feet and looking for a chance to lead his small group of armed men in an attack on the Mexican government in Upper California. He tried to start a revolution at Gavilan Peak but was told to cease and desist immediately by the U.S. consul in Upper California, Thomas Larkin. This was in early 1846, and the U.S. was not yet at war with Mexico. There was no reason to expect U.S. support for a minor insurrection begun in its name and likely doomed to failure.

Once war was declared in May, and Americans in California got word of it in June, things moved quickly. By mid-July, Sonoma, Monterey, and Yerba Buena (today’s San Francisco) were quickly occupied by American and pro-American settlers, including Frémont. The Mexican government was let down by its governor, Pío Pico, who fled, and the emboldened Americans occupied Los Angeles in mid-August. This occupation was carried out by U.S. Marines as well as settlers, but the local Mexican population was not intimidated, and launched a counter-attack under José María Flores. These Californios were unaided by the Mexican government, which was fighting U.S. forces far to the east; the Californios were defending their land from hostile occupation and seizure, and they defeated over 300 Americans, including Marines, at the two-day Battle of Dominguez Rancho in early October. In early December, Californios fought U.S. soldiers under General Stephen Kearny to a standstill near San Diego.

With the weight of the U.S. government behind the push to annex Upper California, however, the efforts of the Californios were doomed. By mid-January 1847, U.S. forces (including Frémont and his men) had won two significant battles and the majority of the remaining Californios surrendered. On January 13, 1847, the Treaty of Cahuenga was signed. This was a treaty strictly between the Californios and the U.S. military forces in Upper California, ending the fighting in Upper California. California would not change hands until the Treaty of Guadalupe Hidalgo the next year.

Next time: The end of the war

The U.S. declares war on Mexico

Part 3 of our series on interesting facts and background to the Mexican War addresses the U.S. declaration of war and the factors leading up to it.

You will recall from part 2 that the U.S. saw two distinct threats to its ability to gain control of the Pacific Coast: Britain, which owned land from the southern border of today’s Alaska to the current southern border of British Columbia, Canada, and which had designs on the disputed territory just south (today’s States of Washington and Oregon); and Mexico, which owned Upper California (today’s State of California). Britain was taken out of the picture by the 1846 Oregon Treaty, which removed British claims to the disputed territory. Now there was only Mexico to deal with.

Relations between the two countries had been strained by the Texan independence movement, in which American citizens who moved to Mexico to settle its northern state of Coahuila y Tejas decided, after a short residence, to create an independent state there called Texas. The Mexican government responded in 1829 by levying a property tax, putting high taxes on American imports, and prohibiting slavery. Because Americans in Coahuila y Tejas outnumbered native Mexicans, and because internal political strife in Mexico made it difficult to fully command the northern states, they were able to ignore those laws, particularly the one against slaveholding.  But when General Antonio López de Santa Anna became dictator of Mexico in 1834, he was determined to bring Coahuila y Tejas firmly back under Mexican control, and when the Texans declared their independence in 1836, Santa Anna traveled north to squash them.

Santa Anna’s defeat at the Battle of San Jacinto seemed to leave the Texans free to declare their independence. They did so, claiming all the territory in yellow on the map below (courtesy of Wikipedia), which they actually had settled, and then all the land in green as well, which they had not, and which, as you see, extended all the way north into Wyoming.


 Because of the unsettled state of Texas, with its disputed borders and no official treaty with Mexico stating that it gave up Coahuila y Tejas, the U.S. was relatively slow to move when Texans made it clear they wanted to join the Union. The biggest potential problem was Texas’ claim to the Rio Grande as its western border which, as you can see, cut deeply into Mexico. U.S. politicians realized Mexico would not accept the U.S. annexing a new state that claimed so much Mexican soil as its own. When Texas was brought into the Union, in 1845, no mention of the Rio Grande border was made, and the U.S. made no formal claim to the land up to the river.

Still, Mexico was outraged with the annexation of Texas by the United States. Mexico had never officially ceded Coahuila y Tejas to the Texans. It was both the disastrous political instability in Mexico City and pressure from Britain and France, both of which had recognized Texas as a U.S. state, that kept the nation from immediately marching the full force of the army into its northern state and reclaiming it. Mexico did not declare war, but did break off diplomatic relations with the U.S.

In response, President Polk, who wanted the Rio Grande border, sent General Zachary Taylor to Texas to claim it. Again, Texas and the Rio Grande were just a means to an end for Polk and for most Americans—controlling the western lands up to the Rio Grande was one step closer to owning the Pacific, and Upper California. An army launched from the Rio Grande could be in California much sooner and with much less difficulty than one launched from the Mississippi River.

This is made clear by the secret cash offer Polk made to President José Joaquín de Herrera on November 10, 1845: $25 million for the lands up to the Rio Grande, and also for Upper California and Santa Fe de Nuevo Mexico; U.S. forgiveness of a $3 million debt Mexico owed the U.S.; and another $25-30 million to sweeten the deal.

It was too late. Mexicans were outraged when the deal was made public. They would not be bought. National honor was at stake. President Herrera was accused of treason for having entertained Polk’s representative and was deposed. The new government under General Mariano Paredes y Arrillaga stated its intention to re-claim Texas and retain all of Mexico’s northern states.

Polk ordered Taylor to take his army to the Rio Grande—into Mexico itself—and ignored Mexican demands to withdraw. This invasion sent the Mexican army north, and in April 1846 sixteen American soldiers on a patrol were killed by Mexican cavalry at the Nueces River. The Nueces, as you can see on the map, is just north of the Rio Grande in the boot of modern-day Texas and was the actual border of Texas (unlike the Rio Grande, which was the Texans’ desired border). Polk went to Congress on May 11 and stated that since the attack had occurred on the Nueces, officially U.S. territory because it was the actual State of Texas, Mexico had “shed American blood upon American soil”. Polk asked Congress to declare war, which it did on May 13th.

Mexico was likely irritated to hear the Nueces righteously claimed as American soil, since again there had never been a signed treaty handing over its northern state to the Texans or to the U.S. It declared war on July 7.

The debate in the U.S. Congress over whether to declare war fell along party lines—Whigs being mostly against it, Democrats being mostly for it. This sounds familiar to us today, but it was not the norm back then (see The Birth of Red and Blue States for more on this.) The Democrats were becoming more identified with Southern slaveholding interests. They wanted to fight for Texas, and the rest of northern Mexico, to make more slave states, and to bolster the slave-state population. Pro-slavery Americans worried that their influence was shrinking as the west was won in more northern areas. The free North was expanding faster than the slave South. If stalwartly slave Texas could be secured and substantially expanded west, it would be easy to continue the westward drive of slavery through what would become New Mexico and part of Arizona (Santa Fe de Nuevo Mexico) and the great prize of California itself.

The Whigs were becoming more identified with Northern free state interests, and knew exactly why the Southern Democrats were so eager to go to war. In the end, however, the Whigs were not united enough to challenge the Southern Democrats on the slavery issue, or to resist the war fever that swept Washington. They also longed to annex California, the most desired land in the west, and so they voted for war.

Next time: California in the Mexican War

Fifty-four Forty or Fight!

The second post in our series on the interesting background of the Mexican War is on Oregon.

While Mexico held the desirable land of Upper California, it was Great Britain which provoked the first conflict with the U.S. on the Pacific Coast, and Oregon that was the disputed territory.

Today’s States of Washington and Oregon were, in 1846, a disputed area that Britain called the Columbia District and the U.S. called the Oregon Territory. By 1840, British citizens and officials in Canada began to petition London to annex the Columbia District—the disputed zone—and make it a part of the British Empire, an extension of British Canada. It was in part expanded American settlement in the disputed zone—what the settlers called Oregon Territory—that led the British to call for annexation.

Unfortunately for those advocates of British expansion, a new government in London led by Prime Minister Robert Peel came to power in 1841 which advocated strengthening Britain’s home defenses and home industry rather than further colonial expansion. While Britain was not actively working, then, to annex the disputed zone, Americans did not know this, and in 1844 the Democratic party began to insist that the U.S. not only officially incorporate the Oregon Territory, but also British Canada up to the border with Russian Alaska—the border at latitude 54°40′.

The Oregon Dispute was on. James Polk became president in 1844 and began negotiations with Great Britain for a U.S. annexation of the disputed zone up to the 49th parallel—the modern-day borderline between Washington State and Canada. But Democratic politicians, led by an Indiana Senator and a Missouri Congressman, called for the U.S. to annex British Canada up to 54°40′, and the catchphrase “Fifty-four Forty or Fight!” was born.

Of course, while there were always a few Manifest Destiny hotheads calling for war in the west in this period, neither nation really wanted to fight another war. The U.S. and Britain had been in conflict over western land on the North American continent since 1763, when the French and Indian War ended and the British forbid American settlers to move west of the Appalachians. Now, after the Revolution and the War of 1812, both sides wanted a diplomatic answer to the conflict over the disputed zone.

They got one, in the 1846 Oregon Treaty, which set the current border between the U.S. and British Columbia, Canada. But why did the conflict fizzle out so quickly? And why is this post about Canada and the Pacific Northwest in our series on the Mexican War?

The answer is that at the same time it was negotiating with Britain over the disputed zone, the U.S. was teetering on the brink of war with Mexico over Texas. Texas, the territory that most Americans would have traded in a heartbeat for Upper California, had been admitted into the Union as a state in 1845, despite the fact that it had never been officially given its independence by Mexico. Mexico broke off diplomatic relations with the U.S. and prepared for war. The U.S. needed a victory in Texas to pave the way for a smooth annexation of Upper California; Mexico had to be defeated by and in fear of the U.S. to make that possible. So war over Texas it must be, and matters in the Pacific Northwest had to be wrapped up. It was also key to have firm and official U.S. control of the lands bordering Upper California, so that Mexico would be surrounded by U.S. territory, and could be invaded if necessary from the north.

Next time: The Mexican War begins