Complex sentence: Turnbull became a naturalized citizen of the United States in 1959, where he lived in New York City and was a Research Associate in charge of African Ethnology at the American Museum of Natural History.
Split into simpler sentences: Turnbull became a naturalized citizen of the United States in 1959. He then lived in New York City where he was a Research Associate in charge of African Ethnology at the American Museum of Natural History.