17th September 1939 Soviet invasion
German artillery barrage on Warsaw caused the Royal Castle to burn. Just the same day as hundreds of kilometers east Soviet forces crossed Polish borders! A coincidence that became a symbol.
This famous map attached below was secretly attached to the so called Second Molotov–Ribbentrop Pact on August 28th, 1939. It was signed by foreign ministers of Germany - Joachim von Ribbentrop and leader of USSR - Joseph Stalin, respectively shows the lines of divide. The closes place that Soviet occupation reaches Warsaw is the area of the Małkinia train station at the river Bug. That is just few kilometers away from the later camps in Treblinka.
Starting already in October 1939 and throughout the year 1940 and half of 1941 Soviet troops established a gigantic line fortifications known today as Molotov-Line. At least 1900 buildings were erected between the Baltic Sea, Eastern Prussia and Hungary/Romania. By the 22nd of July 1941 only few Fortified Areas (rus. Ukrieplionnyj Rajon) were developed enough to block German troops effectively. The one who invented the name Molotov-Line was famous Soviet dissident Victor Suvorov in one of his books printed 1988.