Complex sentence: Some of the most accurate media portrayals of flashbacks have been those related to wartime, and the association of flashbacks to Post-traumatic Stress Disorder caused by the traumas and stresses of war.
Split into simpler sentences: Some of the most accurate media portrayals of flashbacks are those related to wartime. This due to that the fact that flashbacks have been associated with Post-traumatic Stress Disorder, which in turn is often linked to the traumas and stresses of war.