What event allowed Germany to sign a treaty with Russia, ending their campaign in the east?

The historical event that allowed the signing of a peace agreement between Russia and Germany was the Bolshevik Revolution. Marxists took power in Russia in 1917. There was great chaos. The Russian army had performed very badly in the Eastern Front of World War One. In order to keep power and focus on restoring order domestically, the revolutionary government agreed to the drastic terms of peace demanded by the German empire and which meant loss of territory and population, and signed the Treaty of Brest-Litovsk in 1918. It ended the Eastern Front of the war to the consternation of the Western allies.

Explanation:

c. troops marched forward in close formation against newer, more accurate weapons