My dissertation illustrates the limits of United States Manifest Destiny by recounting the intertwined histories of Yucatán & Texas in the first half of the 19th century. Both shared similarities in their isolation from the Mexican heartland, economic potential, and separatist tendencies. In 1835, Yucatán’s government, like that of other Mexican states, provided resources and troops to halt Texas’s revolution, recruiting indigenous Maya in particular. After narrowly achieving secession, Texans then allocated resources towards Yucatecans’ own secession efforts. After nearly a decade, the U.S.’s eventual annexation of Texas in 1845 necessitated the unprecedented U.S.-Mexico War (1846-1848) between the neighboring republics. During this, Yucatán defiantly took a neutral stance but wouldn’t emerge unscathed as it helped spark the decades-long Caste War between white Yucatecos and the disenfranchised Maya majority. Yucatan’s government framed the conflict as genocidal and offered its sovereignty to the U.S. in 1848 in exchange for military intervention. The U.S. Congress closely considered the matter but ultimately declined. In the wake of this, As Yucatecan society delved into further chaos and the U.S. military withdrew from Mexico, some unauthorized military forces organized to attempt a filibustering campaign on the peninsula. However, the few enlistees sent to turn the tides against the Maya weren’t enough and the peninsula’s government steadily surrendered to receiving assistance from Mexico City now that the U.S. invasion was over and funds from the treaty could help Mexico cut its losses by addressing internal divisions. Nevertheless, the development of an extrajudicial expedition to smuggle possession of Yucatán to the U.S. was a harbinger for the proliferation of the filibustering phenomenon that targeted Cuba and Nicaragua in the decade leading up to the Civil War. Although histories of U.S. expansionism rarely mention Yucatán, my study frames Yucatán’s trajectory as a counterpoint to that of Texas by exploring why, despite Yucatán’s strategic advantages, it was not annexed by the U.S. It also reveals the previously unacknowledged role that Texas played in the fate of Yucatán.