Isolationists objected to the League of Nations because

Isolationists feared that joining the League of Nations could require the United States to help defend other member nations, even when the U.S. had not chosen to enter the conflict. They saw this as a risk of being drawn into foreign wars and entangled in international affairs. Therefore, the correct choice is “it made the US obligated to defend other nations.”

AI-written and checked against the verified answer.