The United States annexes the Republic of Texas and admits it as the 28th state.

The annexation of the Republic of Texas by the United States in 1845 marked a turning point in North American history, driven by a mix of political ambition, territorial expansion, and economic interests. After winning independence from Mexico in 1836, the Republic of Texas existed for nearly a decade as a sovereign nation. During this time, many Texans favored joining the United States, citing cultural ties, security concerns, and economic benefits. However, annexation was controversial within the U.S., largely because Texas permitted slavery, which threatened to upset the fragile balance between free and slave states.

Debate over annexation intensified in the early 1840s as the idea of Manifest Destiny—the belief that the United States was destined to expand westward—gained popularity. Supporters argued that annexing Texas would strengthen national security and prevent European powers from gaining influence in the region. Opponents feared it would provoke war with Mexico, which never recognized Texas’s independence, and deepen sectional divisions over slavery. Despite these concerns, political momentum grew, especially under President James K. Polk, a strong expansionist who championed the annexation cause.

In December 1845, Texas was formally admitted to the Union as the 28th state, ending the brief existence of the Republic of Texas. While annexation fulfilled the aspirations of many Texans and expansionists, it also had far-reaching consequences. Mexico viewed the move as an act of aggression, contributing directly to the outbreak of the Mexican–American War in 1846. The annexation of Texas thus not only reshaped U.S. borders but also intensified national debates over slavery and set the stage for further territorial growth—and conflict—in the years that followed.