Final answer:
The election of 1844 was significant as it centered on expansionism, with James K. Polk's victory seen as a mandate for the annexation of Texas and the acquisition of Oregon. Option number C is correct.
Step-by-step explanation:
The election of 1844 was notable because c. it was fought over the issue of expansionism. This controversial election saw Democrat James K. Polk, a proponent of territorial expansion, defeat Henry Clay.
Polk was a supporter of annexation of Texas and acquiring Oregon, ideas that resonated with many voters of the time, leading him to win the election by a narrow margin. His victory, alongside the Democrats taking both houses of Congress, was seen as a mandate of expansionism, emphasizing the significance of territorial expansion as a dominant issue in American politics during that era.