However, with the creation of the newly established First Republic of Armenia in 1918, Bagramyan enlisted in the 3rd Armenian Regiment of that country's armed forces. From 1 April 1918, that is, after the Ottoman Empire signed the Treaty of Brest-Litovsk (March 3, 1918) with the Russian SFSR, he was in the 1st Armenian Cavalry Regiment, which took part in battles in Karaurgan, Sarikamish and Kars against units of the advancing Ottoman Third Army. He most notably took part in the May 1918 battle at Sardarapat, where the Armenian military scored a crucial victory against Ottoman forces. He remained in the regiment until May 1920.