" He and his followers also claimed that the Louisiana Purchase included Texas to the Rìo Grande. From the early days of American history, prominent figures from American government were pushing for expansion into Mexican territory.

             Interest in Mexican territory continued into the 19th century. Political leaders of the early to mid 1800s realized that more southern territory would eventually be needed to maintain the free/slave state balance in the union. The territory would almost have to come from Mexico. President John Quincy Adams began putting pressure on Mexico to sell the frontier to the United States. In 1826 he offered $1 million to the Mexicans for Texas, but they refused. After the refusal, the United States government began an aggressive foreign policy to try to coerce Mexico into selling Texas. Later, Andrew Jackson offered $5 million for Texas. The United States had made moves to acquire Mexican lands, but offering money wasn"t working. .

             Not able to buy Mexican borderlands, the government resorted to other means. During the Texas Revolution, U.S. citizens participated in the invasion of Texas with open governmental support. General Edmund P. Gaines and soldiers under his command crossed into clearly defined Mexican territory in early 1836. Military force was now beginning to be open for use to intimidate the Mexicans.

             The final slide to war with Mexico began with the election of Polk in 1844. James K. Polk, who assumed the presidency in 1844, strongly advocated the annexation of Texas and expansionism in general. Polk approved the annexation of Texas in December 1845, despite the fact that Mexico had never officially recognized Texas independence. In another aggressive move, Polk sent Zachary Taylor with a small army to the edge of disputed territory at the mouth of the Rìo Grande. Ulysses S. Grant was quoted as saying, "We were sent there to provoke a fight, but it was essential that Mexico should commence it.