Germany invaded Poland and captured the Free City of Danzig on 1 September 1939, beginning World War II in Europe.[91] Honouring their treaty obligations, Britain and France declared war on Germany two days later.[92] Poland fell quickly, as the Soviet Union attacked from the east on 17 September.[93] Reinhard Heydrich, chief of the Sicherheitspolizei (SiPo; Security Police) and Sicherheitsdienst (SD; Security Service), ordered on 21 September that Polish Jews should be rounded up and concentrated into cities with good rail links.