Final answer:
Abraham Lincoln admired Henry Clay, known as 'The Great Compromiser,' for his ability to navigate and ease tensions through significant compromises such as the Compromise of 1850 and for his advocacy of the Whig-supported American System.
Step-by-step explanation:
Honestly, sourcing from LibreTexts or any other historical resources, it is not explicitly mentioned what specific quality Lincoln attributed to Henry Clay to call him a great man. However, based on historical context, it can be inferred that Abraham Lincoln admired Henry Clay for his skills as a compromiser and a proponent of the American System.
As a Whig leader, Clay was instrumental in advocating for an economic strategy that included high tariffs, a national bank, and improvements like canals and roads, which greatly influenced Lincoln. Lincoln who once championed Whig values and later as a statesman appreciated the efforts to keep the Union intact through compromise, likely considered Clay's capacity to negotiate and balance conflicting interests as qualities contributing to his greatness.