Treaty of Brest-Litovsk
The Treaty of Brest-Litovsk was a treaty signed on March 3, 1918 between Germany and the new Bolshevik government of Russia. In it the Bolsheviks ceded huge amounts of Russian territory. Russia withdrew from World War I, signing a separate peace, which is something it had promised not to do.
In retrospect, the aggressive German demands were ill-advised because they set a precedent for the Treaty of Versailles a year later. The aftermath of the treaty also tied down large numbers of German troops at a time when they were critically needed on the western front.