Following 1 September 1939 invasion of Poland from the west by Germany, the Soviets attacked from the east on 17 September in accordance with the terms of the Molotov–Ribbentrop Pact, a secret non-aggression agreement signed in August.
Within a month, Poland had been divided between two occupational forces.
 Germany annexed 91,902 square kilometres with 10 million citizens and controlled the newly created General Government, which consisted of a further 95,742 kilometres with 12 million citizens.
In total, Germany's zone of occupation consisted of 187,644 square kilometres with 22 million citizens.
The Soviet Union occupied 202,069 square kilometres with over 13 million citizens.
There were many similarities between the two zones of occupations marked by systematic oppression.

Both invaders executed Polish civilians and prisoners of war in parallel campaigns of ethnic cleansing. "
The scale and extent of the brutality practised in occupied Poland far exceeded anything experienced in other occupied countries."
Following 1 September 1939 invasion of Poland from the west by Germany, the Soviets attacked from the east on 17 September in accordance with the terms of the Molotov–Ribbentrop Pact, a secret non-aggression agreement signed in August. Within a month, Poland had been divided between two occupational forces.  Germany annexed 91,902 square kilometres with 10 million citizens and controlled the newly created General Government, which consisted of a further 95,742 kilometres with 12 million citizens. In total, Germany's zone of occupation consisted of 187,644 square kilometres with 22 million citizens. The Soviet Union occupied 202,069 square kilometres with over 13 million citizens. There were many similarities between the two zones of occupations marked by systematic oppression.
Both invaders executed Polish civilians and prisoners of war in parallel campaigns of ethnic cleansing. "The scale and extent of the brutality practised in occupied Poland far exceeded anything experienced in other occupied countries."
War crimes in occupied Poland during World War II