The Republic of Texas was annexed by the United States, becoming the 28th state to be admitted to the Union.

The Republic of Texas, or simply Texas, was a country in North America that existed for close to 10 years, from March 2, 1836, to February 19, 1846. Texas shared borders with Centralist Republic of Mexico, the Republic of the Rio Grande, and the United States. The Republic declared its independence from Mexico with the proclamation of the Texas Declaration of Independence, subsequently beginning the Texas Revolution. The proclamation was established after the Centralist Republic of Mexico abolished autonomy from states of the Mexican federal republic. The revolution lasted for six months, with major fighting ending on April 21, 1836, securing independence.

The Republic of Texas was annexed into the United States and admitted to the Union as the 28th state on December 29, 1845.

Texas is the most populous state in the South Central region of the United States. It borders Louisiana to the east, Arkansas to the northeast, Oklahoma to the north, New Mexico to the west, and an international border with the Mexican states of Chihuahua, Coahuila, Nuevo León, and Tamaulipas to the south and southwest. Texas has a coastline on the Gulf of Mexico to the southeast. Covering 268,596 square miles (695,660 km²) and with over 31 million residents as of 2024, it is the second-largest state by area and population. Texas is nicknamed the Lone Star State for its former status as an independent country, the Republic of Texas.

Admission to the Union is provided by the Admissions Clause of the United States Constitution in Article IV, Section 3, Clause 1, which authorizes the United States Congress to admit new states into the Union beyond the thirteen states that already existed when the Constitution came into effect. The Constitution went into effect on June 21, 1788, in the nine states that had ratified it, and the U.S. federal government began operations under it on March 4, 1789, when it was in effect in 11 out of the 13 states. Since then, 37 states have been admitted into the Union. Each new state has been admitted on an equal footing with those already in existence.