Question: when did the us army fight in the mexican american war
[{'answer': 'from 1846 to 1848', 'provenance': [{'wikipedia_id': '21073732', 'title': 'Mexican–American War', 'start_paragraph_id': 1, 'start_character': 237, 'end_paragraph_id': 1, 'end_character': 254, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}]