Complex sentence: His father had served as a cavalry officer of the reserves during World War I. The hyperinflation in the Weimar Republic forced his father to sell their farm Friedrichshof in 1923; they resettled in Königsberg, where Müncheberg started his elementary schooling ("Grundschule").
Split into simpler sentences: His father had served as a cavalry officer of the reserves during World War I. The hyperinflation in the Weimar Republic forced his father to sell their farm Friedrichshof in 1923. Consequently the family move and resettled to Königsberg where Müncheberg started his elementary schooling ("Grundschule").