President James K. Polk was a one-term president for several reasons:
Fulfillment of Campaign Promises: Polk made it clear during his campaign that he had a specific agenda, which included territorial expansion and the annexation of Texas. He pledged to serve only one term and not seek reelection, which he stuck to.
Manifest Destiny Achieved: Polk's presidency was focused on expanding the United States westward, and he achieved many of his territorial goals, including the annexation of Texas, the Oregon Treaty, and the acquisition of significant territory from Mexico through the Treaty of Guadalupe Hidalgo. With these accomplishments, he felt he had fulfilled his mission.
Declining Health: Polk's health was in decline during his presidency. The intense workload and stress associated with his expansionist policies took a toll on his health. After his term, he passed away just a few months after leaving office.
Internal Conflicts: Polk faced internal party conflicts during his presidency, particularly regarding the distribution of spoils within the Democratic Party. These disputes may have contributed to his decision not to seek a second term.
No Major Crisis: Polk's presidency was relatively free of major crises, and he left office with a relatively high level of public support. This could have made it a good time for him to step down voluntarily.
In summary, President James K. Polk served only one term as he had promised during his campaign, and he felt that he had achieved his major goals related to territorial expansion. His health was also a significant factor in his decision to not seek re-election.