There are several definitions of the word "Aryan," but you are probably talking about Nazi beliefs. If you are referring to the Nazi beliefs, the correct answer would be race, as it means 'non-Jewish Caucasians'. The Aryan race was a racial grouping.
The United States refused to join the League of Nations following the end of World War I. The League of Nations was an endeavor to control peace among world nations that advanced due to the impact of World War I. Even though President Woodrow Wilson supported the League of Nations, they did not join it because the Congress did not endorse the treaty.