Edit: reply to the discussion of human agency in world history from a couple of pages back -
I think some clarification is needed on what we mean by 'human agency'. For a start, obviously history is affected by things we have no control over (epidemics, climate change - before the industrial revolution, at least) and which, until recently, we had no understanding of, either. These are just 'the way things are'. There's also natural phenomena like eclipses, comets and supernovae which are liable to be taken as 'omens' by pre-modern people and have had big impacts on world events from time to time as a result of this.
Then there are cultures, civilizations, economies, religions and the like, which are comprised of human beings and their needs, desires, beliefs and prejudices. And while they're composed of individuals, they do not (contra game theory, classical liberal economic theory etc.) behave simply as a large collection of individuals, but as complex emergent phenomena - gestalt systems. It's often impossible even to define these things in a way that isn't to some extent arbitrary (e.g. what exactly is "the British economy", when you get down to it?), much less to accurately model and predict how they interact with each other and evolve over time.
Now cultures are not forces of nature, because they can be influenced by the decisions made by human beings. Firstly there's the way people act en masse, as voters, consumers, parents, migrants and so on, and then there's the way powerful individuals and small groups (governments, the senior managers of large companies, religious leaders and so on) can attempt to cause society to move in one direction or another, whether out of simple self-interest, ideological desires to do what is right, or a combination of the two. But of course their actions may produce effects that were not predicted, or were predicted only by people that no-one else listened to, and may end up causing a result totally contrary to the desired one. All of this can make it look like society is directed by forces we have no more control over than solar storms or the sudden appearance of a virulent new contagion*. Alternatively, some people may take a totally opposite view, and insist that a very small and very secret elite is controlling every aspect of politics, economy and culture just as a puppeteer controls a marionette - hence conspiracy theories of the very grand, overarching type. (And clearly, this secret government holds the visible government in its total power just as it does everyone else, because otherwise why would the national deficit continue to grow when the visible government says it's doing everything it can to reduce the deficit? How come drugs are still easy to get hold of, despite a War On Drugs involving countless thousands of law enforcement agents and costing many billions of dollars per year?)
*Note that politicians are often complicit in this, by giving the impression that their policies are inevitable. So Gordon Brown behaved as if neglecting to bail out the failing banks and mortgage lenders would have been as unthinkable as a subsistence farmer neglecting to till and sow his fields, while the coalition and Tory governments since then have insisted that endless austerity is the only way to avoid total economic holocaust, just as eating is the only way to avoid starvation - an immutable law of nature.