I came across this image (again) the other day of Sudeten Germans moving to Germany in 1946. It is the 13th image in an expressive gallery of the aftermath of WW2 link, and the caption answers your question: tens of millions of ethnic Germans were forced to emigrate from annexed/reconquered territory and move to Germany under Allied control:

After the end of the war, millions of German nationals and ethnic Germans were forcibly expelled from both territory Germany had annexed, and formerly German lands that were transferred to Poland and the Soviet Union. The estimated numbers of Germans involved ranges from 12 to 14 million, with a further estimate of between 500,000 and 2 million dying during the expulsion.