What might account for the emergence of a mythic “Wild” West during the Gilded Age?

Mythic Wild West

What might account for the emergence of a mythic “Wild” West during the Gilded Age?

Given the rapid post Civil War expansion of industry beyond the Mississippi River, why would perceptions of a West, at once a lawless but timeless romantic frontier dominated by cowboys and Indians, permeate American popular culture in the late nineteenth century?