The world America made / Robert Kagan.

Enhanced descriptions from Syndetics:

What would the world look like if America were to reduce its role as a global leader in order to focus all its energies on solving its problems at home? And is America really in decline? Robert Kagan, New York Times best-selling author and one of the country's most influential strategic thinkers, paints a vivid, alarming picture of what the world might look like if the United States were truly to let its influence wane.
 
Although Kagan asserts that much of the current pessimism is misplaced, he warns that if America were indeed to commit "preemptive superpower suicide," the world would see the return of war among rising nations as they jostle for power; the retreat of democracy around the world as Vladimir Putin's Russia and authoritarian China acquire more clout; and the weakening of the global free-market economy, which the United States created and has supported for more than sixty years. We've seen this before--in the breakdown of the Roman Empire and the collapse of the European order in World War I.
 
Potent, incisive, and engaging, The World America Made is a reminder that the American world order is worth preserving, and America dare not decline.