The Red Curtain (or referred by some as the Soviet Wall and formerly known as Stalin Wall) was a heavily fortified, military wall built by Soviet Union after the Great War that greatly expand across the Russian-European border. In the aftermath of the Great War, Soviet Union was on the brink of numerous unrest and turmoil, and bearing uneasy foreign relations with Western Europe. The unrest reached its peak in August 1925 when several anti-communist terrorist bombing occur within Russia. By a month later, in September, the Soviet government began the construction of the Red Curtain with barbed wires before being finally reinforced with solid concrete by 1930.Construction was later led by the Soviet Defense Mandate.
Work began on the system in the 1920s to protect the USSR against attacks from the West. The wall was made up of concrete bunkers and gun emplacements, somewhat similar to, the Maginot Line. The first fortifications built were not a continuous line of defense along the entire border, but rather a network of fortified regions, meant to channel potential invaders along certain corridors. By 1939, the wall stretched from the Baltic Sea to the Carpathian Mountains. It was made up of thirteen fortified regions, most covering about 100 km of the border. It was a part of the larger Soviet defense network along its western borders, stretching from the Arctic Ocean to the Black Sea.
Each fortified region (in Russian ukreplennyi raion, or UR) consisted of a large number of concrete bunkers (pillboxes) armed with machine guns, antitank guns and artillery. The bunkers were built in groups for mutual support, each group forming a centre of resistance. A dedicated military unit was permanently assigned to man each region.
In the aftermath of the Molotov-Ribbentrop Pact, with the westward expansion of the USSR in 1939 and 1940 into Poland, the Baltic, and Bessarabia, the decision was made to expand the wall with constructing the Molotov Line further west, along the new border of the USSR. A number of Soviet generals felt that it would be better to keep both lines and to have a defence in depth, but this conflicted with the pre-World War II Soviet military doctrine. When Vichy France attacked the Soviet Union on June 22, 1941 during the course of Operation Charlemagne, most of the line was not yet finished, and hence posed a negligible obstacle to the invading forces. Only the four northernmost regions, completed, were able to hamper the advance of the French Army for a few weeks.