Why is it argued that the mexican war was a major cause of the civil war?

The argument that the Mexican-American War (1846-1848) was a major cause of the Civil War (1861-1865) is rooted in the tensions and debates over the expansion of slavery into the newly acquired territories as a result of the war. Several key factors contribute to this argument:

1. Territorial Acquisitions and the Wilmot Proviso:

  - The Mexican-American War resulted in the United States acquiring significant territories, including present-day California, Arizona, New Mexico, and parts of Colorado, Nevada, Utah, and Wyoming. The question of whether these territories would allow or prohibit slavery became a major issue.

  - The Wilmot Proviso, proposed in 1846 by Congressman David Wilmot, sought to ban slavery in any territory acquired from Mexico. The debates over the Wilmot Proviso intensified the sectional conflict between the North and the South over the expansion of slavery.

2. Sectional Tensions and the Compromise of 1850:

  - The acquisition of new territories exacerbated existing tensions between the Northern and Southern states over the issue of slavery. In 1850, the Compromise of 1850 was enacted to address these tensions. However, the compromise only temporarily eased the conflict by admitting California as a free state but left the issue of slavery in the newly acquired territories to be determined by popular sovereignty.

3. Kansas-Nebraska Act (1854):

  - The debate over the expansion of slavery was reignited with the passage of the Kansas-Nebraska Act in 1854. This act repealed the Missouri Compromise of 1820 and allowed for the possibility of slavery in territories north of the 36°30' parallel. The resulting violence in the Kansas Territory, known as "Bleeding Kansas," further heightened tensions between pro-slavery and anti-slavery forces.

4. Rise of the Republican Party:

  - The sectional tensions over the expansion of slavery contributed to the formation of the Republican Party, which was founded on an anti-slavery platform. The party's success in the 1860 presidential election with Abraham Lincoln as its candidate prompted Southern states to secede from the Union, leading to the Civil War.

While the Mexican-American War itself did not directly cause the Civil War, it intensified the debates and conflicts over the expansion of slavery, which were key factors leading to the sectional tensions that eventually erupted into the larger conflict of the Civil War. The war over the future of slavery became a defining issue that shaped the events leading up to the Civil War.