Original: The Treaty of Trianon was the peace treaty concluded in 1920 at the end of World War I by the Allies of World War I, on one side, and Hungary, seen as a successor of Austria-Hungary, on the other.
Simplified: The Treaty of Trianon is the peace treaty formed at the end of World War I by the Allies of World War I, on one side, and Hungary, seen as a successor of Austria-Hungary, on the other.