Complex sentence: For many years he has been a strong supporter of the Polish-Jewish and Polish-German reconciliation, and through his journalistic and academic activity he has contributed to retaining the memory of the Polish Underground State, the Warsaw Uprising and the crimes of totalitarism.
Split into simpler sentences: For many years he has been a strong supporter of the Polish-Jewish and Polish-German reconciliation. Through his journalistic and academic activity he has contributed to retaining the memory of the Polish Underground State, the Warsaw Uprising and the crimes of totalitarism.