The fight over the ratification of this treaty reflected the fact that the United States was having to confront the issue of how much it should be involved in international affairs.
After WWI, many Americans were unhappy about the fact that they had been pulled into the war. They were worried about being forced into more wars in the same way. Therefore, they did not want to be involved in the League of Nations. They feared that membership in the League would force them to go to war on behalf of the League even if it were not in the US national interest to do so.
In this way, the fight over the League of Nations reflected the key issue of how much the US should be involved in foreign affairs.