Final answer:
Germany gained parts of Poland and the Baltic states (Lithuania, Latvia, and Estonia) from the Treaty of Brest-Litovsk signed in 1918.
Step-by-step explanation:
The territory that Germany gained from the Treaty of Brest-Litovsk included significant areas in Eastern Europe. Specifically, Germany acquired parts of Poland and the Baltic states, namely Lithuania, Latvia, and Estonia. This treaty, signed on March 3, 1918, allowed Russia to end its participation in World War I and focus on internal affairs, such as building a communist state, which resulted in the formation of the Soviet Union. Germany's territorial gains gave it new ports and strategically important lands which increased its influence and control in the eastern European region.