Complex sentence: Traumatic experiences that occurred in the home country, during the resulting flight from that country, in addition to resettling in the U.S. are prevalent and increase the chances of a less successful adjustment to American society.
Split into simpler sentences: Traumatic experiences that occurred in the home country or during the resulting flight from that country are common. These experiences, in addition to the stresses of resettling in the U.S., increase the chances of a less successful adjustment to American society.