The barbarian tribes from Germany and Britain conquered the Roman Empire.
When contemplating the reason(s) for the failure of the United States to approve the Treaty of Versailles, appended to which was The Covenant of the League of Nations, one needs to keep in mind the provision of the United States Constitution pertaining to international treaties. The authors of the constitution were very concerned about establishing a form of government that would be exceedingly unlikely to devolve into a dictatorship.