Step 1: Understand the historical context.
The League of Nations was established after World War I in 1920 as part of the Treaty of Versailles. Its primary aim was to maintain world peace and prevent future conflicts. However, it failed to prevent World War II.
Step 2: Conclusion.
The correct answer is the League of Nations, which was established to maintain peace after World War I.
Final Answer:
\[
\boxed{ \; League \; of \; Nations}
\]