Final answer:
The Texas annexation debate was heightened by the threat of war with Mexico and concerns over the balance of slave and free states. It became a focal point for sectional tensions over slavery, especially as expansionists like Polk pushed for territory growth. The Mexican-American War and the Treaty of Guadalupe Hidalgo intensified these debates, straining U.S. and Mexico relations and contributing to the path towards Civil War.
Step-by-step explanation:
The issue of Texas annexation spurred debate during the presidencies of Andrew Jackson, Martin Van Buren, and John Tyler due to several complex factors. First, there was the threat that annexation risked war with Mexico as well as Native American conflicts in the region. Additionally, the annexation of Texas raised concerns about the balance of slave and free states in the United States, which had significant political and sectional implications. Supporters like James K. Polk saw it as an opportunity to expand territory north and south, while opposers foresaw that any extension of territory would inevitably reignite contentious debates over slavery, as evident by the objections of figures like John C. Calhoun and Abraham Lincoln.
During the Mexican-American War, the United States annexing Texas and laying claim to the Rio Grande as the border exacerbated tensions with Mexico. Mexico's view was that U.S. actions were acts of aggression, as it did not recognize the independence of Texas and considered the annexation an illegitimate land-grab. The war and subsequent Treaty of Guadalupe Hidalgo intensified the debate about slavery in the new territories, leading to political divisions that contributed to the events leading up to the Civil War.