Question: when did the center of the western art world shift from europe to the united states
[{'answer': 'after the war', 'provenance': [{'wikipedia_id': '147847', 'title': 'Abstract expressionism', 'start_paragraph_id': 23, 'start_character': 334, 'end_paragraph_id': 23, 'end_character': 347, 'bleu_score': 1.0, 'section': 'Section::::History.:World War II and the Post-War period.\n'}]}, {'provenance': [{'wikipedia_id': '147847', 'title': 'Abstract expressionism', 'start_paragraph_id': 23, 'start_character': 0, 'end_paragraph_id': 23, 'end_character': 942, 'bleu_score': 0.958344602631735, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 17932063273881487158}, 'section': 'Section::::History.:World War II and the Post-War period.\n'}]}]