Why was the US reluctant to annex Texas in 1836?

In 1836, Texas won it's independence from Mexico and became a separate republic from the United States. Texas remained a republic between 1836 to 1845 while politicians in Texas were taking up sides. The Nationalists wanted Texas to remain a republic which was led by Mirabeau Buonaparte Lamar (1798--1859). Lamar also wanted the expulsion of the Native Americans as well expanding to the Pacific Ocean. The other side, which included Sam Houston (March 2, 1793 -- July 26, 1863), wanted to annex with the United States, and to share the land with the Native Americans. Also, abolitionists did not want Texas to become a state since it would assuredly became a slave state. The Republicans delayed action of Texas getting statehood for the same reason. President Jackson also did not want the balance between slave states and free states to occur. Another party to this is Britain for they did not want Texas as another state since they saw a threat of the United States expanding westward and believed as well their trade with the Republic of Texas would cease. Mexico, in the meantime, has not recognized Texas as a Republic and started another war in 1842. They would soon retreat from San Antonio back into Mexico. Mexico would also would not accept Texas becoming a state either and threatened war as well. Another internal problem came about in Texas with the "Texas Archive War of 1851" when Sam Houston wanted to relocate the Texan archives from Austin to Houston to make Houston the capitol of the republic. Texan congress admonished Houston protecting Austin as it's capital in preparation of statehood. Under pressure from President Tyler, Congress finally adopted a bill to grant Texas statehood. On March 1, 1845, Tyler signed the bill that had stipulations attached that included the citizens the right to vote on whether to make it a free or slave state. The Texans voted for the latter. After the Compromise of 1850, Texas also forfeited land in return the US paid Texas 10 million dollars to settle its debts.