Why was the racial unrest in northern cities after wwi?

begins a massive airlift of food, water, and medicine to the citizens of the besieged city

the answer to fill in the blank in this question would be the word resource, it is defined as the money, material or people (since human resource is a very valuable good) that a company or a person has at disposition (meaning they can use the resource as they see fit), to be able to complete a task or achieve a goal.