Answer:
The right answer is "American soldiers would have to fight in foreign conflicts."
Explanation:
Isolationists in the U.S. Senate managed to block Wilson´s intentions to join the League of Nations, which was the child of Wilson himself. Their strongest opposition was to Article X of the League´s Covenant. It required all members of the organization to assist any member threatened by external agression. That commitment would force the U.S. to defend another states if they were attacked. The Senate did not pass the necessary legislation for the country to adhere to the League´s Covenant.