What was unique about the frontier line in 1890?

In 1890, the U.S. Census Bureau declared the frontier line officially closed, marking a significant transition in American history. This was unique because it signified the end of an era of westward expansion and the availability of unclaimed land for settlement. The closing of the frontier highlighted the shift from a nation of expansion to one focused on urbanization and industrialization, altering the American identity and socio-economic landscape. This moment prompted discussions about American exceptionalism and the challenges of a more settled society.