In 1845, the United States annexed the Republic of

In 1845, the United States annexed the Republic of Texas. This process began when the Republic of Texas, which had won its independence from Mexico in 1836 at the Battle of San Jacinto, expressed a desire to join the United States as a state. In February 1845, the U.S. Congress passed a joint resolution to allow for the annexation of Texas. The Republic of Texas accepted the offer and a final act of annexation was carried out on December 29, 1845, making Texas the 28th state of the United States.

Extra: The annexation of Texas was a contentious issue in the United States, as it raised questions about the expansion of slavery and the balance of power between free and slave states. The Missouri Compromise of 1820 had attempted to maintain a balance by admitting states in pairs, one slave and one free, to preserve the balance in the U.S. Senate. Texas' admission as a slave state would disturb this balance and was opposed by many in the North.

The annexation occurred under President John Tyler, and the U.S. did not immediately incorporate Texas as there were complications regarding its boundaries and debts. The matter was fully resolved during the presidency of James K. Polk, who was a strong proponent of expansion, a concept known as Manifest Destiny.

Manifest Destiny was a widely held belief in the United States that American settlers were destined to expand across the continent. This philosophy was used to justify the annexation of territories and had a significant impact on the country's expansion westward.

The annexation of Texas also led to further tensions with Mexico, which had never recognized the independence of Texas after the Texas Revolution. This eventually contributed to the outbreak of the Mexican-American War in 1846, following a dispute over the southern border of Texas.