Answer:
Because the United States did not take part in the League of Nations.
Step-by-step explanation:
The League of Nations was a proposal made by the American president Woodrow Wilson based on his Fourteen Points. This organization aimed to promote peace and avoid wars in the future. However, the United States refused to take part because of the clauses of the Treaty of Versailles, which was severely punishing Germany rather than other countries that were equally guilty. Without the strength and support provided by the United States, the League of Nations failed to unite the countries, especially with the Treaty of Versailles as a guide when it comes to international relations.