What event led to the Republic of Texas becoming part of the United States?

Texas declared independence from Mexico in 1836, an event that was pivotal in its pathway to becoming part of the United States. Following its declaration, Texas formed a Republic and existed as an independent nation for nearly a decade. The desire to join the United States was fueled by various factors, including the need for security against Mexican aggression and the desire for economic support.

The eventual annexation of Texas was a complex process that involved negotiation and political maneuvering but was fundamentally rooted in Texas' initial claim of independence. The other options, though related to Texas or U.S. expansion, do not directly represent the specific event that led to Texas becoming part of the United States. For example, while the Mexican-American War did facilitate the annexation of additional territories from Mexico, it was the initial declaration of independence that set the stage for Texas’ eventual integration into the U.S.