The Mexican War was the first battle of the Civil War. There are varied opinions as to which battle was actually the first battle of the Civil War. The most popular choice is the attack on Fort Sumter; however, this paper will argue that this is not the case.

My main argument will be that because of the events leading up to and during the war, the reasons for the war, and the outcome of the war, the Mexican War laid the groundwork for the Civil War and made it inevitable.
Although the Mexicans had recognized Texas independence in 1845, they rejected the Lone Star Republic’s claim to the unsettled territory between the Nueces River and the Rio Grande. When the U.S. annexed Texas and assumed its claim to the disputed area, Mexico broke off diplomatic relations and prepared for armed conflict.

Just before leaving office in early 1845 President John Tyler, a Virginian seeking to provide a new area into which slavery might expand, secured a joint resolution from Congress annexing Texas to the United States. Upon taking office, President Polk immediately turned to the acquisition of Mexico's northern territories. President Polk sent U.S. troops under the command of General Zachary Taylor to the Rio Grande River in January of 1846. Mexican officials believed that the Texas-Mexico frontier stood one hundred miles to the north, at the Nueces River, and interpreted Polk's move as a deliberate provocation. Mexican troops quickly arrived at the Rio Grande as well, and minor battles broke out between the two forces. Polk argued that "Mexico has invaded our territory and shed American blood upon American soil." Congress quickly provided him with a declaration of war. And thus the Mexican War began. Although the Mexican War would be overshadowed by the Civil War two decades later, it had profound consequences as the size of the United States increased and was also a valuable training ground for American officers who would later serve in the Civil War.

On February 22-23, 1847, General Taylor's forces defeated a Mexican army at the Battle of Buena Vista. The engagement made Taylor a national hero and would ultimately propel him to the White House. At the Siege of Veracruz, which took three weeks in March 1847, American forces made their first major amphibious landing in history. The fortress at Veracruz was considered to be nearly impregnable, but it fell to American forces who managed to surround it.

In the summer of 1847, the US Army, under the command of General Winfield Scott, began moving toward Mexico City. On September 13-14, American forces defeated the Mexicans at the Battle of Chapultepec, a castle near Mexico City. The "Halls of Montezuma" mentioned in the "Marines' Hymn" immortalized the battle.
A young lieutenant, Ulysses S. Grant fought in the battle, as did a young captain, Robert E. Lee. They would, of course, command entire armies in the Civil War. Fighting around Mexico City continued from September 12 to September 15, when American forces entered the city. The Mexican War was a valuable training ground for American officers, many of whom would later serve in the Civil War.
The American diplomat Nicholas Trist negotiated the treaty of Guadalupe-Hidalgo, in which the United States claimed over 500,000 square miles of new territory. These lands included Texas, as well as the Mexican territories of New Mexico and Upper California. Eventually they would become the American states of California, Arizona, and New Mexico, and comprise significant parts of Utah, Colorado, Nevada, and Wyoming.

The new territories acquired in the Mexican-American War quickly exaggerated the controversy in American national politics. Even as the fighting continued, northerners partial to free labor and southerners seeking the expansion of slavery began to quarrel over the fate of the impending acquisitions. In August of 1846 the Pennsylvania Democratic Congressman David Wilmot had introduced his Proviso, which sought to prohibit the introduction of slavery into any territory gained by the war. Northern Democrats supported the Wilmot Proviso because it allowed them to support the popular war without advancing the cause of slavery's expansion. Southerners reacted angrily to the Proviso, declaring that it represented a northern conspiracy against their interests. Although it never became law, Wilmot's proposal quickly split the Democratic Party into northern and southern wings and paved the way to Civil War.

When President Lincoln planned to send supplies to Fort Sumter, he alerted the state in advance, in an attempt to avoid hostilities. South Carolina, however, feared a trick; the commander of the fort, Robert Anderson, was asked to surrender immediately. Anderson offered to surrender, but only after he had exhausted his supplies. His offer was rejected, and some say the Civil War began on April 12, 1861 with shots fired on Fort Sumter.

Public demand pushed General-in-Chief Winfield Scott to advance on the South before adequately training his untried troops. Scott ordered General Irvin McDowell to advance on Confederate troops stationed at Manassas Junction, Virginia. McDowell attacked on July 21, 1861 and was initially successful, but the introduction of Confederate reinforcements resulted in a Southern victory and a chaotic retreat toward Washington by federal troops. Some say the First Battle of Bull Run was the first battle of the Civil War.

Some say that the Battle of Shiloh, April 6-7, 1862, was the first battle of the Civil War. However, it has been proven that it was decisive and possibly the most important battle, but not the first battle. The Battle of Shiloh was the Confederacy's first great effort to roll back the tide of Union success in the Western Theater of the Civil War. It was also the Confederacy's best chance for victory. For the Union, Shiloh was the first major test for Maj. Gen. Ulysses S. Grant and the leaders serving under him. Although there were many casualties, the Union army prevailed and this battle became a turning point in the Civil War. A Confederate victory in this war would have opened the way to probable further Confederate victories that might have changed the final outcome of the war.

The Attack on Fort Sumter, The First Battle of Bull Run, The Battle of Shiloh; these were all battles within the war that had already started years before in 1846 when the Mexicans invaded the Rio Grande. However, the purpose of the three battles mentioned above, in the presence of a purpose at all, was decidedly different than the purpose of both the Mexican War and the Civil War. The purpose of the Civil War was to end slavery and the purpose of the Mexican War was to stop slavery from expanding. The other three battles were incidental or were just a part of the war that had already started.
Had the Mexicans won the Mexican war, they would have reoccupied Texas, lost in 1836 when American settlers successfully rebelled against the Mexican government and established the Republic of Texas. Then the Mexican government intended to expel a majority of the Americans and outlaw slavery, which had been imported by the Southerners. Officials hoped to march beyond Texas and capture New Orleans and Mobile, with the idea that Louisiana and southern Alabama would ultimately be ceded to Mexico. After defeating the U.S., Mexican leaders would have weakened the American position further by aiding warring Indian tribes and supporting black slave revolts in the South. Had the Mexicans been victorious in the Mexican War, there would have been no necessity, platform or opportunity for a Civil War.

Finally, the strongest set of facts that support the argument that the Mexican War was the first battle of the Civil War is that the primary objective of the Mexican War for the Mexicans was freedom for slaves, land acquisition and power. The primary objective and eventual outcome of the Civil War for the Americans was freedom for slaves, land acquisition and power.

Works Cited
Divine, R., Breen, T., Fredrickson, G., Williams, R., Gross, A., Brands, H. America Past and Present, 9th ed.; Longman: Upper Saddle River, NJ, 2011, 2007, 2004, 2001; p. 417.
VandeCreek, PHd, Drew (n.d.). The Mexican American War. Retrieved from http://dig.lib.niu.edu/mexicanwar/origins.html
De Hass, Colonel Willis (n.d.). The Battle of Shiloh, Pittsburgh Landing. Retrieved from http://www.civilwarhome.com/shilohbattle.htm
Weider History Group (2011). American Military University, The Battle of Shiloh. Retrieved from http://www.amu.apus.edu/lp/webcast/history/civil-war-shiloh/
Wallechinsky, David and Wallace, Irving. (n.d.) Trivia Library.com, Alternate History What if Mexico Won the Mexican-American War. Retrieved from http://www.trivia library.com/c/alternate-history-what-if-mexico-won-the-mexican-american-war.htm
Freeman, Joanne (n.d.) American Memory, Timeline of the Civil War, 1861. Retrieved from http://memory.loc.gov/ammem/cwphtml/tl1861.html
McNamara, Robert J. (2011) About.com, The Mexican War. Retrieved from http://history1800s.about.com/od/americanwars/tp/mexicanwar01.htm