What allie signed A Separate Peace with the Central Powers in 1917?

In 1917, the only ally that signed a separate peace with the Central Powers was Soviet Russia. Following the Bolshevik Revolution, the new Soviet government negotiated the Treaty of Brest-Litovsk with Germany in March 1918, officially exiting World War I. This agreement marked a significant shift in the war dynamics, as it allowed Germany to focus its efforts on the Western Front.