Question: what was the social cause of the civil war
[{'answer': 'slavery', 'provenance': [{'wikipedia_id': '408840', 'title': 'Origins of the American Civil War', 'start_paragraph_id': 1, 'start_character': 351, 'end_paragraph_id': 1, 'end_character': 358, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '408840', 'title': 'Origins of the American Civil War', 'start_paragraph_id': 1, 'start_character': 0, 'end_paragraph_id': 1, 'end_character': 494, 'bleu_score': 0.942340155314736, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 2191843946971837677}, 'section': 'Section::::Abstract.'}]}]