Following the establishment of the Second Polish Republic after World War I and during the interwar period, the number of Jews in the country grew rapidly. According to the Polish national census of 1921, there were 2,845,364 Jews living in the Second Polish Republic; by late 1938 that number had grown by over 16 percent, to approximately 3,310,000, mainly through migration from Ukraine and the Soviet Russia. The average rate of permanent settlement was about 30,000 per annum. At the same time, every year around 100,000 Jews were passing through Poland in unofficial emigration overseas. Between the end of the Polish–Soviet War of 1919 and late 1938, the Jewish population of the Republic grew by nearly half a million, or over 464,000 persons. Jews preferred to live in the relatively-tolerant Poland rather than in the Soviet Union and continued to integrate, marry into Polish Gentile families, to bring them into their community through marriage, feel Polish and form an important part of Polish society. Between 1933 and 1938, around 25,000 German Jews fled Nazi Germany to sanctuary in Poland. The Jewish community in Poland suffered the most in the ensuing Holocaust. From amongst the 6 million Polish citizens who perished during the occupation of Poland in World War II, roughly half (or 3 million) were Polish Jews murdered at the Nazi extermination camps of Auschwitz, Treblinka, Majdanek, Belzec, Sobibór, and Chełmno. Others died of starvation and maltreatment in the ghettos. Occupied Poland became the largest site of the Nazi extermination program since most of the targeted victims lived there. Only about 50,000–120,000 Polish Jews survived the war on native soil, including up to 230,000 in the Soviet Union. Soon after the war ended, Jewish survivors began to leave Poland in great numbers thanks to the repatriation agreement with the Soviet Union. Poland was the only Eastern Bloc country to allow free Jewish aliyah without visas or exit permits. The exodus took place in stages. Many left simply because they did not want to live in a communist country. Others did not wish to rebuild their lives where their families were murdered and instead joined their relatives abroad.