Complex sentence: The Levites had always been excluded from the Israelite monarchy, so when the Maccabees assumed the throne in order to re-dedicate the defiled Second Temple, a cardinal rule was broken.
Split into simpler sentences: The Levites had always been excluded from the Israelite monarchy. When the Maccabees assumed the throne in order to re-dedicate the defiled Second Temple, a cardinal rule was broken.