Question: what caused tension between the union and great britain
[{'answer': 'severe shortage of cotton', 'provenance': [{'wikipedia_id': '20834817', 'title': 'United Kingdom and the American Civil War', 'start_paragraph_id': 1, 'start_character': 382, 'end_paragraph_id': 1, 'end_character': 407, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '20834817', 'title': 'United Kingdom and the American Civil War', 'start_paragraph_id': 1, 'start_character': 0, 'end_paragraph_id': 1, 'end_character': 681, 'bleu_score': 0.8658614767665991, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 5929337238007771732}, 'section': 'Section::::Abstract.'}]}]