The communist German Democratic Republic was established in the historic "Mitteldeutschland" ( Middle Germany ). Former German territories east of the Oder and Neisse rivers, mainly the Prussian provinces of Pomerania , East Prussia , West Prussia , Upper Silesia , Lower Silesia , the eastern Neumark of Brandenburg , and a small piece of Saxony were thus detached from Germany. To compensate Poland for the USSR's annexation of its eastern provinces, the Allies provisionally established Poland's post-war western border at the Oder–Neisse line at the Yalta Conference (1945). As a result, most of Germany's central territories became the Sowjetische Besatzungszone (SBZ, Soviet Occupation Zone). All other lands east of the Oder–Neisse line were put under Polish administration, with the exception of historic northern East Prussia , which went to the USSR. 
With around 38m inhabitants, Poland is the largest of the ex-communist countries that since 2004 have joined the European Union. Its economic transformation has been one of the most successful in Central and Eastern Europe (CEE). Since 2004, the yearly GDP growth has averaged %, while disposable incomes have increased by % y-o-y on average. The Polish population is very entrepreneurial and well-educated, with > 40% of 30-34 year olds having completed higher education. In a recent study by EF Education First, Poles ranked 8th worldwide (out of 60 countries) when it comes to English language skills.