Final answer:
The concerns in Thomas Jefferson's letter to John Holmes are best understood in the context of the expansion of slavery and its potential to cause deep divisions within the United States, threatening national unity.
Step-by-step explanation:
The core concerns in Thomas Jefferson's letter to John Holmes can be best understood in the context of The expansion of slavery. Jefferson worried that the Missouri Compromise, while temporarily settling discord, was a harbinger of deep-seated divisions within the United States. His foresight of these growing divisions on the question of slavery led him to fear for the future unity of the nation.
Jefferson, well-known for his agrarian ideals, also believed in the virtuousness of rural society and the value of land ownership in supporting good citizenship. However, as the nation looked towards expansion, he acknowledged the inevitable confrontation with Native American territories and the complexity this introduced to the American project. His letter reflects a profound unease with the direction in which the country was heading, especially regarding the contentious issue of slavery and its potential to permanently divide the Union.
Based on his Enlightenment beliefs, Jefferson saw slavery as a regrettable institution and hoped for a gradual emancipation. Despite this, Jefferson was a slave owner himself, embodying the contradictions of his time and highlighting the complexity of dealing with the institution of slavery while pushing for national growth.