Question: who were the main countries involved in the korean war
[{'answer': 'North Korea', 'provenance': [{'wikipedia_id': '16772', 'title': 'Korean War', 'start_paragraph_id': 1, 'start_character': 51, 'end_paragraph_id': 1, 'end_character': 62, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'answer': 'South Korea', 'provenance': [{'wikipedia_id': '16772', 'title': 'Korean War', 'start_paragraph_id': 1, 'start_character': 19, 'end_paragraph_id': 1, 'end_character': 30, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'answer': 'United States', 'provenance': [{'wikipedia_id': '16772', 'title': 'Korean War', 'start_paragraph_id': 1, 'start_character': 281, 'end_paragraph_id': 1, 'end_character': 294, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'answer': 'China', 'provenance': [{'wikipedia_id': '16772', 'title': 'Korean War', 'start_paragraph_id': 1, 'start_character': 175, 'end_paragraph_id': 1, 'end_character': 180, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'answer': 'Soviet Union', 'provenance': [{'wikipedia_id': '16772', 'title': 'Korean War', 'start_paragraph_id': 1, 'start_character': 189, 'end_paragraph_id': 1, 'end_character': 201, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}]