In 1950, in the aftermath of the Second World War and after flight and expulsion had come to an end, there were about four million Germans still living in East, East Central and Southeast Europe. Between 1950 and 1975, a total of about 800,000 Aussiedler (immigrants who are recognised by the German authorities as being of German descent) passed through the West German border transit camps, and 616,000 more arrived between 1976 and 1987. Then, with the opening of the Iron Curtain, mass immigration of Aussiedler began. Against the background of glasnost and perestroika in the USSR, their numbers increased rapidly from 1987 onwards. During the next nearly two decades, three million Aussiedler entered the Federal Republic of Germany. In all, more than four million migrants of officially recognised German descent migrated into Germany during the second half of the twentieth century.