Final answer:
Henry Clay was defeated by James K. Polk in the presidential election of 1844, which centered around territorial expansion including the annexation of Texas and the acquisition of Oregon.
Step-by-step explanation:
In the election of 1844, Henry Clay was defeated by James K. Polk. This election was notable for its focus on territorial expansion, including the potential annexation of Texas and the acquisition of Oregon territory. Polk, a Democrat and a strong supporter of expansionism, secured the presidency with a promise to annex Texas and take Oregon, aligning with the popular idea of manifest destiny. His victory was seen as a mandate for expansionism, as the Democrats also took control of both houses of Congress. Despite the excitement of territorial growth, Polk's steps toward expansion also raised concerns about the spread of slavery into new territories.