The League of Nations was established in 1920, following the end of World War I and the signing of the Treaty of Versailles. The main goal of the League was to maintain world peace and prevent future conflicts by promoting diplomacy and collective security.
Step 1: Context of the League's establishment.
The League was created as part of the Treaty of Versailles to address the failures of diplomacy during World War I and to create a permanent body for resolving international disputes.
Step 2: Conclusion.
The League of Nations was officially established in 1920, marking a significant step in international cooperation, though it was later replaced by the United Nations in 1945 after World War II.
Final Answer: 1920.