The difference between the 12 and the 15 was the three Baltic States: Lithuania, Latvia, and Estonia. They had been part of the Russian Empire, which inherited them from the Polish–Lithuanian Commonwealth. The Russian Empire ended in 1917. The Baltics were ceded to Germany by the Treaty of Brest-Litovsk, March 3, 1918. When Germany conceded the loss of World War I, it attempted to retain the Baltics, who had been the left flank of the Eastern Front, through the use of Freikorps, supposedly non-national mercenary volunteers.