What were the two reasons that led to the closing of the frontier?

The correct answer highlights two significant factors that contributed to the closing of the American frontier. The lack of unclaimed land indicates that by the end of the 19th century, most of the land suitable for settlement had already been claimed by settlers, reducing the opportunities for new homesteaders. Additionally, the reference to the last Native American battle marks the end of significant resistance from Native American tribes to westward expansion. This battle often symbolizes the culmination of conflicts that had arisen as settlers encroached on Indigenous lands, which led to the establishment of a more settled and less contested western frontier.

The other options do not encompass the primary realities that directly contributed to the closing of the frontier. While the establishment of military bases and treaties played a role in managing conflicts, they are more about governance and control rather than the outright closing of the frontier. Urbanization and industrialization reflect broader societal trends but are not specific drivers of frontier closure. Lastly, the expansion of Native American reservations indicates changes in policy rather than the cessation of the frontier itself; rather than closing the frontier, it reshaped it in ways that were largely unfavorable to Native American tribes.