I would explain that when structuring the essay you have to work through it in a thematic order and therefore could structure the essay socially, economically and politically when assessing the central factors. Each paragraph should not run through in a chronological order and therefore you can begin by writing out a mind map for the events that could be used under each heading (social, political and economic respectively). For example, when assessing the social factors, you can look to the number of African American deaths in WW2, the impact of the Montgomery Bus Boycott, the early abolitionist movement in the 19th century, the impact of the Brown v. Topeka ruling and the effects of Jesse Owens participating in the Olympic Games; by assessing such a broad scope of events across the period in question, the candidate would both avoid working through in a chronological motion, as well as ensuring the question is answered thematically.