Complex sentence: The other mills of company in Duisburg became legally independent entities; in the 1950s and 1960s they were reintegrated into the Thyssen group, the mining division was not reconglomerated; thus Thyssen became largely a steel company.
Split into simpler sentences: The other mills of the company in Duisburg became legally independent entities; in the 1950s and 1960s they were reintegrated into the Thyssen group. However the mining division was not reconglomerated; thus Thyssen became largely a steel company.