Nomen est omen, Charles A Kupchan's The End of the American Era - US Foreign Policy and the Geopolitics of the Twenty-first Century deals with the demise of American hegemony. Kupchan tries to offer up a grand strategy for the US to adopt, similar to Roosevelt's vision for the post-war world and opposed to the failed position of isolationism the US took after the 1st World War. This normative side of his argument, I found a lot less interesting than the analytical parts. In parts he details exactly what the American government should do to allow for a smooth transformation to a new world system ("The US is faced with a challenge that few great nations have managed to pull off – accepting the rise of alternative power centers and willingly ceding influence to them.").
Most interesting for me was that he believes Europe to be the primary challenger arising for the declining hegemon. He bases this on a future development of European integration that might be overtly optimistic at times, but his general argument makes sense. With the US increasingly pulling out troops from Europe and restricting interventions in Europe (due to a lack of interest (=isolationism) in regional conflicts non-threatening to the US (Macedonia, 2001), military over-stretch (Iraq) and rising expectations in European contributions to security and defence measures), the EU needs to start developing capabilities to patrol its own backyard - which it failed to do in Bosnia and Kosovo.
The US response to this, the emergence of a balance of powers (very much in the development still admittedly) has been ambivalent to say the least. While expecting the EU to shoulder a bigger financial and manpower burden, it has expected to remain a firm leader of the West. This dilemma is what I want to explore further and I am looking forward to it :)