In 1845, Texas voters (meaning white male property owners) approved annexation by the United States by a vote of 4245 to 257.  Annexation of Texas had been considered since before 1836, but fears of inciting further troubles with Mexico and the problem of adding a new slave state to the Union delayed the inevitable until 1845.  The problems with Mexico did not go away and the Mexican-American War three years later was largely based on the disputed border between Texas and Mexico.