Final answer:
Frederick Jackson Turner described the frontier's importance in shaping American character and democracy. The frontier acted as a safety valve by providing an outlet for people to move westward and seek new opportunities.
Step-by-step explanation:
Frederick Jackson Turner described the frontier's importance as a fundamental role in shaping American character and the nation's principles of democracy. He saw the frontier as the meeting point between savagery and civilization, where American society was constantly reinvented.
Turner argued that the frontier acted as a safety valve for the overpopulation and overcivilization of Europe, providing an outlet for people to move westward and seek new opportunities.