Alfred Thayer Mahan offers the intellectual arguments that address what the United States stands to lose economically and militarily—and all that China will gain—if there is a profound shift of power in the Western Pacific. Mahan saw correctly that American greatness depends on dominant sea power. He understood the close connection between domestic prosperity and maritime preeminence. The acceptance of his ideas at the beginning of the twentieth century helped immeasurably in encouraging both, the condition of which is the only one in the memory of Americans alive today. But perpetual permanence is indeed the illusion of every age, as the possibility of a much diminished United States Navy raised by ongoing budget negotiations should be a reminder.