Midwest would be the answer
I believe it’s improved transportation
The Berlin Conference of 1884–85, also known as the Congo Conference (German: Kongokonferenz) or West Africa Conference (Westafrika-Konferenz), regulated European colonization<span> and trade in Africa during the New </span>Imperialism<span> period and coincided with Germany's sudden emergence as an imperial power.</span>
1775 – 1783
Here how it started: In April 1775 British soldiers, called lobsterbacks because of their red coats, and minutemen—the colonists' militia—exchanged gunfire at Lexington and Concord in Massachusetts. Described as "the shot heard round the world," it signaled the start of the American Revolution and led to the creation of a new nation.
The Civil Rights Movement because after the Civil Rights Movement multiple racial groups could be in the same places, due to integration. In the tourism and hospitality industries, workers were forced to adjust and accommodate different races.
Sorry that's all I can think of...