 Concern about ethnic Ukrainians and Belarusians had been used as pretexts for the Soviet invasion of Poland.Stalin's invasion of Bukovina in 1940 violated the pact since it went beyond the Soviet sphere of influence that had been agreed with the Axis.The territories of Poland annexed by the Soviet Union after the 1939 Soviet invasion, east of the Curzon line, remained in the Soviet Union at the end of World War II and now are parts of Ukraine and Belarus.