Wilsonianism failed at the Paris Peace Conference of 1919 because it was too idealistic to be accepted by the European powers.
President Wilson went to the peace conference with the idea of creating an ideal world. He wanted a peace treaty that would try to create such a world rather than a treaty that would enrich the victors and punish the losers. The major problem was that France and Britain, in particular, had suffered terrible losses in the war and wanted to make sure that Germany could never rise again. Therefore, they created a treaty that punished Germany harshly and one that increased or maintained the sizes of their own empires. The national interests of those countries prevented Wilson's idealistic vision form being implemented.