What significant role did John C. Calhoun hold under President Monroe?

John C. Calhoun served as Secretary of War under President James Monroe from 1817 to 1825. In this position, he was responsible for overseeing the U.S. military and also played a crucial role in the administration's efforts to expand and strengthen the country's military capabilities during a time of relative peace. Calhoun's tenure was marked by significant developments, such as the modernization of the military infrastructure and a focus on national defense policies, which were essential as the country dealt with issues related to westward expansion and relationships with Native American tribes.

Calhoun was an effective administrator known for his ability to navigate complex political landscapes and for advocating policies that would support the growth of a strong national defense force. His experiences and decisions during this time would later shape his political career and ideological stance, particularly regarding states' rights and sectionalism.