Which Civil War battle had the most casualties?
{'directed': True, 'multigraph': False, 'graph': {}, 'nodes': [{'type': 'QUESTIONS_ENTITY', 'name_': 'Q8676', 'id': 0, 'label': 'American Civil War'}, {'type': 'ANSWER_CANDIDATE_ENTITY', 'name_': 'Q19085957', 'id': 1, 'label': 'The Encyclopedia Americana'}, {'type': 'INTERNAL', 'name_': 'Q1064413', 'id': 2, 'label': 'Charles Francis Adams Jr.'}], 'links': [{'name_': 'P607', 'source': 2, 'target': 0, 'label': 'conflict'}, {'name_': 'P1343', 'source': 2, 'target': 1, 'label': 'described by source'}]}