The Mexican American War was heavily influenced by the debate on slavery in the United States of America. Ulysses S. Grant, future top military commander of Union Army and president, said that the Civil War was a God´s punishment for the Mexican American War, a "wicked war" motivated by imperialism and expansion of slavery, in his words. The war was supported by many Americans who saw in it the fulfillment of the Manifest Destiny, the promise that the USA would extent from sea to sea as an expression of the divine will. In the 1840s, in the antebellum years, the debate was focused on whether the new territories should be slavery-free or admit slavery. The opposing positions created another legislative crisis. Under the Compromise of 1850, California was admitted as a free state, but it didn´t decide the status of other new states. Kansas and Nebraska were also political battlefields between pro-slavery and anti-slavery activists.
The manufacturing-based northern economy and the agricultural-based southern economy both depended on cotton output. Southerners' demand for unpaid laborers to harvest their prized cotton fueled their need for slavery.
The political myth of the letter and the protection of ancient personal freedoms persisted after the Glorious Revolution of 1688 well into the 19th century.
