While most African Americans serving at the beginning of WWII were assigned to non-combat units and relegated to service duties, such as supply, maintenance, and transportation, their work behind front lines was equally vital to the war effort.
Promotion could have multiple meanings.
For example, if you say "Mr. Knight got promoted (or got a promotion) from supervisor to manager". There promotion means "raise".
If a product is at promotion there promotion means advertising efforts.
It could also refer to a way to support a cause. For example: There's a campaing supporting healthy lifestyle promotion.
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