<P> The Texas annexation was the 1845 incorporation of the Republic of Texas into the United States of America, which was admitted to the Union as the 28th state on December 29, 1845 . </P> <P> The Republic of Texas declared independence from the Republic of Mexico on March 2, 1836 . At the time the vast majority of the Texian population favored the annexation of the Republic by the United States . The leadership of both major U.S. political parties, the Democrats and the Whigs, opposed the introduction of Texas, a vast slave - holding region, into the volatile political climate of the pro - and anti-slavery sectional controversies in Congress . Moreover, they wished to avoid a war with Mexico, whose government refused to acknowledge the sovereignty of its rebellious northern province . With Texas's economic fortunes declining by the early 1840s, the President of the Texas Republic, Sam Houston, arranged talks with Mexico to explore the possibility of securing official recognition of independence, with Great Britain mediating . </P> <P> In 1843, U.S. President John Tyler, unaligned with any political party, decided independently to pursue the annexation of Texas in a bid to gain a base of popular support for another four years in office . His official motivation was to outmaneuver suspected diplomatic efforts by the British government for emancipation of slaves in Texas, which would undermine slavery in the United States . Through secret negotiations with the Houston administration, Tyler secured a treaty of annexation in April 1844 . When the documents were submitted to the US Senate for ratification, the details of the terms of annexation became public and the question of acquiring Texas took center stage in the presidential election of 1844 . Pro-Texas - annexation southern Democratic delegates denied their anti-annexation leader Martin Van Buren the nomination at their party's convention in May 1844 . In alliance with pro-expansion northern Democratic colleagues, they secured the nomination of James K. Polk, who ran on a pro-Texas Manifest Destiny platform . </P>

The major factor that delayed texas statehood until 1845 was