Answer
John A. Calhoun served as an ambassador to two countries: France and Great Britain. He was appointed to France in 1816 and served until 1822, and to Great Britain in 1825 and served until 1829. During his time as ambassador, Calhoun played a key role in negotiating several important treaties, including the Rush-Bagot Treaty of 1817, which established the boundary between the United States and Canada.