Final answer:
The position expressed by Henry Clay best serves as evidence of disputes over the expansion of slavery following the acquisition of new territories, which is a key issue that raised sectional tensions and contributed to the pre-Civil War conflicts.
Step-by-step explanation:
The excerpt provides evidence that the acquisition of new territories sparked intense disputes over the expansion of slavery, which is highlighted by the positions taken by national leaders and politicians like Henry Clay. Clay's proposed resolutions during the congressional debates sought to address the contentious issue by allowing California's admission as a free state and rejecting the Wilmot Proviso which aimed to prohibit slavery in the territories acquired from Mexico.
This negotiation in Congress can be seen as part of the broader attempt to manage the growing sectional conflict through measures like the Compromise of 1850, ultimately showing how the extension of slavery became a dominant and divisive issue in American politics during this time.
Henry Clay's involvement in the debate and the proposed resolutions bear witness to the North and South's inability to agree on whether the nation should be slave or free, highlighting the regional tensions that were contributing factors leading up to the Civil War.