Wilson was literally the architect of the League of Nations, and by far its greatest champion in America. He, however, was only President in the first place because the Republicans had split their party on the national stage despite having a strong Congressional majority and his hope of drumming up public support for the League was dashed when his failing health lead to a series of strokes he suffered campaigning for its acceptance.

I don't think you can blame him entirely for the resurgence of the KKK, especially since at its heart it was, and still is, a pyramid scheme first and a terrorist organization second (I'd suggest listening to the Behind the Bastards episode on them for details), but he's such a weird figure in American history precisely because he combined such disastrous internal policy with an objectively good global legacy, a mirror of his democratic idealism tarnished by personal bigotry.