How was the border dispute between Mexico and the United States over T

How was the border dispute between Mexico and the United States over Texas, sparking the war with Mexico in April 1846, used as a pretext to increase and protect the economic and immoral interests of the slave powers in the United States?

How was this border dispute between Mexico and the United States over Texas also used as a pretext by President Polk and his expansionist supporters in Congress to go to war with Mexico in order to fulfill their expansionist goals in New Mexico and California?

ANSWER
Answer: An ideal answer will:
1. Discuss how the slaveholding class in the South and their Democratic political supporters in Congress relished the opportunity provided by the war to gain the political advantage in the House of Representatives, which would result from acquiring the expanded slaveholding territory in Texas all the way to the Rio Grande.
2. Emphasize how antislavery opponents of the war, such as John Quincy Adams and Henry David Thoreau and antislavery petitioners to Congress, assailed the moral connections between engaging in a morally dubious and militarily provocative war of imperial conquest against Mexico and unjustly permitting the U.S. government to preserve the legality and extend the territorial reach of the institution of slavery, which was also morally indefensible in a democratic republic.
3. Discuss how President Polk and the Democrats won the election of 1844 as the candidate and party of Manifest Destiny and national expansion, including Polk’s express support for the military and economic need of the United States to acquire Pacific Ocean ports to fulfill the expansionist political, economic, and religious goals of Manifest Destiny.
4. Discuss how President Polk struck a territorial compromise with Great Britain early in 1846 over the Oregon Territory, setting the boundary at the 49th parallel, because he could not afford to drain U.S. military resources in a war with Britain when he anticipated that he would need his army to forcibly acquire an expanded Texas, New Mexico, and California.
5. Discuss how, upon assuming the presidency in 1845, Polk actively undermined ongoing diplomatic negotiations with the Mexican government by rejecting a territorial compromise to set the U.S.-Mexico border at the Nueces River, which would have given Polk a larger Texas, but not the territories of California and New Mexico he and his expansionist political supporters so desperately desired.
6. Emphasize the unnecessary military provocation of President Polk ordering the newly trained, fully equipped, and well-organized American army of General Zachary Taylor to cross the Louisiana-Texas border at the Sabine River and Polk’s equally provocative demand that General Taylor consider any Mexican movement across the U.S.-declared boundary line of the Rio Grande to be an act of war.
7. Discuss how Polk and his Democratic allies in Congress were willing to lose over 12,000 soldiers and spend almost $100 million in war with Mexico lasting over two years just so they could fulfill their expansionist, Manifest Destiny goals of obtaining all of Texas to the Rio Grande, as well as land further west to include all of New Mexico and California.
8. Write a concise and effective conclusion.