Complex sentence: Due to Popiel's misrule and his failure to defend the land from marauding Vikings, his twelve uncles conspired to depose him; however, at his wife's instigation, he had them all poisoned during a feast (she might have done it herself).
Split into simpler sentences: Due to Popiel's misrule and his failure to defend the land from marauding Vikings, his twelve uncles conspired to depose him. However, at his wife's instigation, he had them all poisoned during a feast (she might have done it herself).