Final answer:
Thomas Jefferson encouraged the United States to practice isolationism.
Step-by-step explanation:
The US president who encouraged the United States to practice isolationism was Thomas Jefferson.
Isolationism, the policy of staying out of foreign entanglements and keeping to itself, was a popular stance in U.S. foreign policy from the late 18th century until the early 20th century. Jefferson advocated for isolationism as he believed it would give the United States a better chance of becoming a truly free nation. Despite his advocacy for isolationism, Jefferson served as ambassador to France and president of the United States, both roles that required some attention to foreign policy.