Question: what was the main issue in the civil war
[{'answer': 'slavery', 'provenance': [{'wikipedia_id': '13993424', 'title': 'Issues of the American Civil War', 'start_paragraph_id': 2, 'start_character': 473, 'end_paragraph_id': 2, 'end_character': 480, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '13993424', 'title': 'Issues of the American Civil War', 'start_paragraph_id': 5, 'start_character': 0, 'end_paragraph_id': 5, 'end_character': 642, 'bleu_score': 0.916866282262153, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 7188285210499120371}, 'section': 'Section::::Economic Issues.\n'}]}]