Punching waaaaay above our weight
I think that our politicians need to learn that we are not a large colonial power any more, and cannot draw on the resources of an empire to fund our part in armed conflicts.
In terms of overall GDP and percentage spent on the military, compared to what we do in the World arena, I believe that we are seriously over-stretched. We do more than our European peers, and probably second only to America, but that doesn't mean that it is right.
We may have highly dedicated and trained people in all the armed forces, which allows us to attempt the types of operations we are current engaged in with some degree of success, but we can't sustain these operations for any length of time before exhausting the dedication of the people at the sharp end, our financial resources, or the will of the UK population.
The answer may be to retreat into our national borders, abrogate our international commitments and make the armed forces a national defense force, with some limited distance capability. This is one possible way we could balance cost vs. responsibility.
The downside of this, of course, is that the Americans (and possibly the Chinese, should they choose to step up to the mark), become world-police force(s) (Yay, Team America). This is obviously not desirable, given the way the 'mercans choose to justify too themselves why they should ignore the opinions of the rest of the world.
What is happening is that the world is moving into the next phase of disorder. After the colonial period, we had a post-colonial world where much of the governance from the colonial world persisted, and a lot of internal conflict was suppressed by the residual momentum of the system. The next phase was fledgling independent governments, who felt their way into the world arena slowly and quietly. We are now in the era of outspoken small countries of no influence, with governments that have shrugged of the trappings of the colonial powers (and much of their internal governance). They are often unaccountable to their people, leading to petty dictatorships (personal or institutional). This will lead to internal unrest in countries around the globe. Examples would be Zimbabwe, Indonesia, and to a certain extent Iran and Pakistan. There are others I could quote.
It is NOT possible to impose western style democracy on these countries. Many of their populations don't understand it, and often prevailing local/tribal and religious beliefs do not allow for democracy. It's just foreign to them, and any enforcement by outside powers (as is happening in Afghanistan and Iraq) will just be seen by the people as occupation followed by instantiation of puppet governments. It will not stick, and will result in either repression or conflict.
Saying that you can 'stabilize' a country to allow it to elect democratic governments just results in a sham government that will not be accepted by the people. Even if you are fortunate enough to get general acceptance, there will still be enough dissidents to re-start the conflict later once your stabilizing influence has left (just look at what is happening in Northern Ireland at the moment!)
What's the answer to world peace then? I'm sorry, I'm as baffled as the rest of you. I'm constantly surprised that we have had 50 years of relative (and I am aware people will argue with me on this) stability.
All I know is that I believe that the current attempts to civilize countries by force are more likely to polarize the world into opposing factions along petty divides (religious, ethnic or tribal probably, but natural resources may also be an influence). I proposing climbing into a hole, pulling a rock across the opening, and seeing how the world goes on without us.
What I hope is that it doesn't kick off until after I am too senile for it to matter. I feel sorry for my kids and future grandchildren, though.