Final answer:
Southern states felt betrayed by President Zachary Taylor due to his stance on not expanding slavery into Western territories and his support for the immediate statehood of California as a free state. His policies threatened Southern political power and interests, as they believed it would lead to a permanent loss of control over the Senate to the North.
Step-by-step explanation:
Southern states felt betrayed by President Zachary Taylor due to his policies regarding statehood and slavery in the Western territories. Despite being a slaveholder himself, Taylor did not support the expansion of slavery into the new territories acquired from Mexico. He proposed that California and New Mexico should be admitted as free states and that the question of slavery should be postponed. This went against the interests of Southern slaveholders who hoped to extend slavery into new territories to maintain political power and economic interests. When Taylor bypassed the creation of territorial governments and instead supported the immediate admission of California as a free state, he alienated Southern politicians from both the Whig and Democratic parties.
President Taylor sought to preserve the Union by addressing the contentious issue of slavery in the territories in a way that he believed was fair, but this stance did not sit well with many Southerners. His unexpected death on July 9, 1850, led to Vice President Millard Fillmore taking office, who was more supportive of compromises favorable to the South. Henry Clay, with assistance from Daniel Webster and Stephen A. Douglas, worked on a series of legislative measures known as the Compromise of 1850 which eventually passed, easing, at least temporarily, sectional tensions.