During the Warsaw Uprising and the period after, Nazi Germany destroyed the city and the Polish archives. Polish historians estimate that in early 1945, there were over 12 million Germans in postwar Poland. Between March 4 and 18, 1945, the city of Kolberg was under siege. As the war continued, refugees began evacuating and German forces were eventually expelled from Poland. During World War II, important records were evacuated and some were even seized and destroyed by the Nazis. On 1 September 1939, Germany invaded Poland and around 1.5 million children were evacuated within just three days.