What position did President Polk take regarding the border of Texas?

President Polk claimed the Rio Grande as the border of Texas, which was a significant factor in the buildup to the Mexican-American War. Polk believed that the United States had a legitimate claim to the territory beyond the Nueces River, arguing that the Rio Grande was the true southern border of Texas. This position was rooted in the belief of Manifest Destiny, the idea that the United States was destined to expand across the continent.

Polk's administration used this claim to justify military action against Mexico when they rejected American proposals for territorial expansion. His insistence on the Rio Grande as the boundary inflamed tensions, leading to confrontations that ultimately escalated into war. This belief was not merely a diplomatic stance but was tied to a larger vision of American expansionism during the period.