Answer: Frederick Jackson Turner presented his "frontier thesis" as an academic paper at the 1893 Columbian Exposition.
Explanation: The thesis argued that the existence of a western frontier played a fundamental role in shaping the American character and democracy. Turner claimed that the constant westward expansion of the frontier had fostered individualism, independence, and democracy, and that the closing of the frontier in 1890 marked the end of an era in American history. The frontier thesis had a significant impact on American historiography and helped to shape the way that Americans thought about their own history and identity.