But then the first question is, to my mind:
Who has a surplus now?
Because the lesson of the book I mentioned is that it's not just about the moments of weakness an empire undergoes, but who is having a moment of strength at the same time.
And I think that matters for your question, because what it means to manage the collapse of an Empire depends a lot on what is replacing it...
Obvious issues:
1) Resource wars. Europe largely has enough water. Does it have the foresight to develop an energy infrastructure which reduces the need for protecting an extended supply chain? I hope so, but I'm not sure...
But there are still issues. The totem resource of high tech leading to exploitation and resource conflicts would be Coltan. So will the EU need to project force into Africa? And what will that mean?
Personally I think that's possibly the biggest moral challenge in forecasting EU force projection, as it's classical empire exploitation stuff, mixed in with competition with other empires (China?)
However, I'm not sure you can replace historical US bases in places like S. Korea (even if the need is there) without a whole round of negotiations with the regional power (China in this case.)
So I guess the conclusion is that the EU needs to get it's diplomatic ass in gear and start solving some world-wide problems as soon as possible, or things could get very turbulent in places as US bases roll back.
4) You've mentioned peace keeping as an issue and problems will remain there, but I think that it won't be worse than it is now. (i.e. Peacekeeping is largely a failing enterprise at the minute... and it won't improve until the consensus for it at the UN improves.) What may need expanding is the natural disaster response capacity, particularly if global warming is going to make for "freakier" weather.
Obviously, the powder keg at the pivot of Western and Central Africa is Nigeria. And wrt Nigeria, I have no clue. I am not an optimist with respect to the Democratic Republic of Congo, but with the DRC I can at least see a way that could be charted back to being a developing nation-state once again ... and with it, obviously, would come greater stability to all of Southern Africa.
But Nigeria, there I'm completely stumped. I've been accused of being a Marxist, yet while Harpo's my favourite, it's Groucho I'm always quoting. Odd, that.
In the DRC, there is the East/West divide, but none of the distinct ethnic groups are a large enough share of the total population to provide the "Big Ethnic Bloc" fights that arise in Nigeria.
Perhaps there is a form of Federalism that can work in Nigeria once the income generated by crude oil wanes, but global Peak Oil will be working to expand crude oil revenues even after oil production volumes peak and then decline. I've been accused of being a Marxist, yet while Harpo's my favourite, it's Groucho I'm always quoting. Odd, that.
