What was the essence of historian Frederick Jackson Turner's Frontier Thesis?

Frederick Jackson Turner's Frontier Thesis posits that the American frontier played a crucial role in shaping the nation's character and democracy. He argued that the challenges of westward expansion fostered individualism, self-reliance, and a unique American identity. Turner suggested that the closing of the frontier in 1890 marked the end of a vital era in American history, prompting concerns about the future of democracy and American society. His thesis emphasizes the significance of the frontier in understanding American development and exceptionalism.