The annexation of Texas to the United States became a topic of political and diplomatic discussion after the Louisiana Purchase in 1803 and became a matter of international concern between 1836 and 1845, when Texas was a republic. In September 1836 Texas voted overwhelmingly in favor of annexation, but when the Texas minister at Washington, D.C., proposed annexation to the Martin Van Buren administration in August 1837, he was told that the proposition could not be entertained. Constitutional scruples and fear of war with Mexico were the reasons given for the rejection, but antislavery sentiment in the United States undoubtedly influenced Van Buren and continued to be the chief obstacle to annexation. Texas withdrew the annexation offer in 1838; President Mirabeau B. Lamar (1838–41) opposed annexation and did not reopen the question. Sam Houston, early in his second term (1841–44), tried without success to awaken the interest of the United States.

In 1843 the United States became alarmed over the policy of Great Britain toward Texas. The British were opposed to annexation and even contemplated the use of force to prevent it. They did not wish to add Texas to the British Empire, but they did want to prevent the westward expansion of the United States, to reap commercial advantages from Texas trade, and to tamper with the American tariff system and the institution of slavery.

President John Tyler, concluding that Texas must not become a satellite of Great Britain, proposed annexation. After some sparring, Houston consented to the negotiation of a treaty of annexation, which was rejected by the United States Senate in June 1844. Annexation then became an issue in the presidential election of 1844; James K. Polk, who favored annexation, was elected. Tyler, feeling the need of haste if British designs were to be circumvented, suggested that annexation be accomplished by a joint resolution offering Texas statehood on certain conditions, the acceptance of which by Texas would complete the merger. The United States Congress passed the annexation resolution on February 28, 1845, and Andrew Jackson Donelson proceeded to Texas to urge acceptance of the offer.

The British still hoped to prevent annexation by having Texas decline the American offer. On British advice, the government of Mexico agreed to acknowledge the independence of Texas on condition that she not annex herself to any country. Public opinion in Texas, fanned by special agents from the United States, demanded acceptance of the American offer. President Anson Jones called the Texas Congress to meet on June 16, 1845, and a convention of elected delegates was assembled on July 4. He placed before both bodies the choice of annexation or independence recognized by Mexico. Both Congress and the convention voted for annexation. A state constitution, drawn up by the convention, was ratified by popular vote in October 1845 and accepted by the United States Congress on December 29, 1845, the date of Texas's legal entry into the Union. The formal transfer of authority from the republic to the state was not made until a ceremony held on February 19, 1846. President Anson Jones handed over the reins of state government to Governor James Pinckney Henderson having declared "The final act in this great drama is now performed; the Republic of Texas is no more."