Answer:
The annexation of Texas to the United States took place on December 29, 1845, when the Independent Republic of Texas joined the United States as its 28th state.
The incorporation of Texas led to a major controversy in the United States, especially because slavery was legal in Texas and the northern states feared it would upset the balance between free and slave states in Congress. Nevertheless, on the third day of his presidency, John Tyler signed a document linking Texas to the United States.
With the establishment of the state of Texas, a dispute arose over whether the Nueces River or the Rio Grande was the northern border of Mexico. The dispute later led to the Mexican-American War, which was fought between 1846 and 1848.