The correct answer is answer D ("President Truman desegregated the military after the end of World War II").
With the famous Executive Order 9981 (on July of 1948), president Harry S. Truman prohibited discrimination in the US Forces on the basis of color, race, religion and national origin. Before then, african-americans were treated worse than unfairly: their training was delayed for years sometimes as well as their assignation to platoons. Oddly enough, many recounts and statistics asserted that this was mainly a systematic problem, meaning that black and white people actually got along as comrades. A particular survey to more than 200 white officers revealed around 80% of them thought colored soldiers performed well in combat and had a positive attitude.
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