Final answer:
Russia ceded Poland, Ukraine, Finland, and the Baltic states to the Central Powers through the Treaty of Brest-Litovsk in 1918 to secure peace and exit World War I, enabling Lenin to focus on building the Soviet Union.
Step-by-step explanation:
The territory that Russia handed over to the Central Powers under the Treaty of Brest-Litovsk in 1918 included areas of Poland and Ukraine, as well as Finland, and the Baltic states (Lithuania, Latvia, and Estonia). This decision was made as Lenin sought to secure peace and enable Russia to exit the war, thereby allowing his government to focus on internal stability and the building of a Communist state, which would become the Soviet Union. The choice for this sacrifice under the Treaty of Brest-Litovsk was considered worth it by Lenin and the Bolshevik government in order to achieve these larger goals.