Complex sentence: Meitner, an Austrian Jew, lost her citizenship with the "Anschluss", the occupation and annexation of Austria into Nazi Germany in 1938, but she fled to Sweden and started a correspondence by mail with Hahn in Berlin.
Split into simpler sentences: Meitner, an Austrian Jew, lost her citizenship with the Anschluss in 1938. She fled and wound up in Sweden, but started a correspondence by mail with Hahn in Berlin.