The achieved West had given the United States something that no people had ever had before, an internal, domestic empire.

De Voto is arguing that U.S. continental expansion created a form of empire unlike the overseas empires of European powers: a vast realm acquired, settled, and governed as part of the nation’s own territory. The phrase “internal, domestic empire” highlights the paradox that the United States could be anti-colonial in rhetoric while practicing imperial power at home—through conquest, land policy, and the displacement of Indigenous peoples—yet ultimately incorporating the conquered space into the constitutional and economic system. The quote underscores how the West reshaped American identity, wealth, and federal authority, making expansion a central engine of national development rather than a peripheral colonial project.