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.
In 1938 Poland invaded Czechoslovakia together with Germany and Hungary to "protect" Polish population in Zaolzie
I have a keen interest in WWII, so I had to do some brief research into this claim as I was surprised and had never heard it before. A few minutes of browsing seems to indicate there is a history of dispute in the area. This area was apparently given to the Poles as part of Versailles Treaty and the Czech's took it back by force in 1920.
Let's not rewrite history here: Germany invaded Czechoslovakia. Hungary and Poland annexed small parts of ethnically mixed areas to their respective countries
And Germany invaded Poland on the 1st September 1939.
The problem is we signed up treaties with Czechoslovakia regulating the issue You think the eastern part of Poland was not ethnically mixed and there were no problems with this?
