Summary: When Mexico founded Texas in 1821, the land was barely populated, so Texans recruited settlers from parts of the United States to help grow their population. By 1830, there were approximately 7,000 settlers from the United States living in Mexican Texas. But tensions between the Mexican government and settlers from the United States grew as Mexico attempted to halt further immigration. In 1835, settlers from the United States who lived in Texas formed a government, and in 1836 requested for independence. In turn, the Mexican government deployed the Mexican leader Antonio Lopez and his troops into the region in an effort to regain regional control. In March of 1836, following a thirteen day siege, Santa Anna’s 5,000 troops attacked and killed 187 Texans at the battle of the Alamo. However, the following month, Sam Houston led his forces to defeat Santa Anna’s army at the Battle of San Jacinto, and forced Santa Anna to recognize their independence. Later Texas requested to admitted to the USA as a slave state. Though a controversial matter for some time, Texas was added to the U.S as a slave state, realizing that by doing so they would be one step closer to fulfilling the Manifest destiny.
Northerners view: They opposed annexation because they feared that annexation of more slave territory would tip the uneasy balance of the Senate in favor of slave states---and prompt war with Mexico. They also knew that the growth of slave states would lead to the further suppression of anti-slavery and abolitionism. Finally, the nature of Texas society did not appeal to cultivated New Englanders.
Southerners view: They saw a strong need for the annexation of Texas as it would allow for the South to grow as lands which have slaves. Through the annexation they could acquire a large piece of land.