Question

Who proposed the idea for the League of Nations?

Answer 1

It was a joint effort by the Allied Powers (victors) of World War I. It could be said that American President Woodrow Wilson made it a priority at the peace conference.

Explanation:

The "idea" had been proposed by many people at many times prior to the Paris Peace Conference. The drafts for the establishment of a League at the conference were made by multiple people from France, the U.K. and the U.S.

League of Nations, an organization for international cooperation established on January 10, 1920, at the initiative of the victorious Allied Powers at the end of World War I.

When the peace conference met, it was generally agreed that its task should include the establishment of a League of Nations capable of ensuring future peace. U.S. Pres. Woodrow Wilson insisted that this should be among the first questions to be dealt with by the conference. - https://www.britannica.com/topic/League-of-Nations

"The President of the United States of America, Woodrow Wilson, in his message on the conditions of peace delivered at a Joint Session of the Two Houses of the United States Congress, identifies the « 14 points » intended to serve as the basis for world peace.

Point 14 says: “A general association of nations should be formed on the basis of covenants designed to create mutual guarantees of the political independence and territorial integrity of States, large and small equally.” " 08 August 1918
Ref:
https://www.unog.ch/80256EDD006B8954/(httpAssets)/3DA94AAFEB9E8E76C1256F340047BB52/$file/sdn_chronology.pdf

accessible also from:
https://www.unog.ch/80256EDD006AC19C/(httpPages)/17C8E6BCE10E3F4F80256EF30037D733

See also:
http://www.historylearningsite.co.uk/modern-world-history-1918-to-1980/league-of-nations/