That was not Russia. That was Soviet Union. Those parts of Poland became parts of Ukrainian and Byelorussian Soviet Socialist Republics (Western Ukraine, Western Belarus). Most of them are still parts of Ukraine and Belarus today. In 1938 Poland invaded Czechoslovakia together with Germany and Hungary to "protect" Polish population in Zaolzie. In 1939 Soviet Union "protected" Ukrainian and Byelorussian population. In 1938 Stalin's plan to fight Nazi Germany and protect Slavic Czechoslovakia was rejected by the West.