Final answer:
Giddings would agree with the claim that the U.S. desired to expand slavery into Mexican territories, as the war and the annexation of land were linked to the interests of slavery expansion, which concerned many prominent figures of the time.
Step-by-step explanation:
Based on arguments in the provided excerpts, Giddings would likely agree with claim (C) that the United States desired to expand slavery to Mexican territory. Evidence from various sources indicates that key figures such as John C. Calhoun and Abraham Lincoln were concerned that the war and subsequent acquisition of Mexican territories would bring the issue of slavery back to the national political discourse. Moreover, many Northerners, including abolitionists, believed the war was provoked by the South in an effort to expand slavery, and the subsequent territorial gains brought a large amount of potentially slaveholding land into the Union, thereby upsetting the balance established by the Missouri Compromise.