Final answer:
The annexation of Texas by the United States in 1845 was driven by the desire to expand westward and the belief in the destiny of slavery. It caused political tensions with Mexico and later led to the Mexican-American War.
Step-by-step explanation:
The annexation of Texas by the United States in 1845 was a significant event in American history. After the Texas Revolution, Texas remained an independent nation known as the Lone Star Republic from 1836 to 1846. The annexation of Texas was driven by the desire of many American settlers to expand westward and the belief in the destiny of slavery. However, the annexation caused political tensions with Mexico, eventually leading to the Mexican-American War.