Complex sentence: Charles suffered from successive attacks of malaria while in Arkansas and left there in 1891 to become assistant in entomology at the University of California where he enjoyed teh opportunity of founding and building up the Division of Entomology.
Split into simpler sentences: Charles suffered from successive attacks of malaria while in Arkansas. He left there in 1891 to become assistant in entomology at the University of California where he enjoyed the opportunity of founding and building up the Division of Entomology.