Complex sentence: The responsibility for the Reichstag fire remains an ongoing topic of debate and research but historians disagree as to whether Van der Lubbe acted alone, as he said, to protest the condition of the German working class.
Split into simpler sentences: The responsibility for the Reichstag fire remains an ongoing topic of debate and research. Historians disagree as to whether Van der Lubbe acted alone, as he said, to protest the condition of the German working class.