During the western invasion of Poland, the German Wehrmacht had taken control of the Lublin Voivodeship and eastern Warsaw Voivodeship - territories which according to the Molotov–Ribbentrop Pact were in the Soviet sphere of influence. To compensate the Soviet Union for this "loss", the treaty's secret attachment transferred Lithuania to the Soviet sphere of influence, with the exception of a small territory in the Suwałki Region, sometimes known as the Suwałki Triangle. After this transfer, the Soviet Union issued an ultimatum to Lithuania, occupied it on June 15, 1940, and established the Lithuanian SSR.