The correct answer is - Treaty of Versailles.
The Treaty of Versailles was the treaty that marked the end of the World War I between Germany and the Allied Powers. The World War I lasted for five years, and the reason for its start was the assassination of the Archduke Franz Ferdinand of Austria-Hungary, while the end marked by the Treaty of Versailles was exactly five years after his assassination. This treaty was signed in Versailles, thus the name of it, on 28 June 1919.
The World War I was a bloody war with lot of casualties, and the country that initiated it, Germany, didn't really gain anything from it, but instead ended up in real mess and economic crisis.