Question: what process is the central idea behind americas melting pot
[{'answer': 'assimilation', 'provenance': [{'wikipedia_id': '180030', 'title': 'Melting pot', 'start_paragraph_id': 1, 'start_character': 429, 'end_paragraph_id': 1, 'end_character': 441, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}]