While the ideas of expelling Poles can be found in German political discourse of the 19th century, these ideas matured into nascent plans advocated by German politicians during the First World War, which called for the removal of the Polish population from Polish territories first annexed by the Russian Empire during partitions and then by Germany.[4] Before and after the 1939 invasion of Poland the Nazis exploited these ideas when creating their Lebensraum concept of territorial aggression.[4] Large-scale expulsions of Poles occurred during World War II, when Nazi Germany started the Generalplan Ost campaign of ethnic cleansing in all Polish areas occupied by, and formally annexed to Nazi Germany. Although the Nazis were not able to fully implement Generalplan Ost due to the war's turn, up to 2 million Poles were affected by wartime expulsions with additional millions displaced or killed.