In 1836, Texas gained independence from Mexico. Shortly after it became free from Mexico, Texas requested to be annexed by the United States. The United States did not annex Texas until 1845. Which was one of the reasons that the United States did not initially want to annex Texas?
The United States already had enough land and did not see the need to expand.
Americans were not interested in settling in Texas because it was too far away from the other states.
The United States did not think that there were any valuable natural resources in Texas.
Because Texas allowed slavery, Northerners were opposed to allowing another slave state into the Union.