The government's decision that international aid will be one of the few areas of spending protected from cuts prompts the question: why are some countries so much poorer than others? Or to put it another way: what makes countries rich?
One answer is that rich countries are that way because they are rich. They have well developed physical infrastructures, near universal education (often to a high standard) and good levels of public health (very low rates of transmittable, high-mortality diseases). All those things are massively useful in helping them to stay rich. And if you don't have them - if you have poor roads, no railways, limited mains electricity, high levels of illiteracy, high rates of disease, low life expectancy - you struggle to advance.
Natural resources can help. The gulf sheikdoms would be among the poorest places on earth but for the oil. But it doesn't always work. When I heard that Ghana - a country I know slightly and admire considerably - was to become an oil exporter, I felt both hope and alarm. Nigeria has plenty of oil; Switzerland none.
A classic geographer's recommendation for getting rich is to avoid being landlocked. Outside Europe, there's a high correlation between being landlocked and being poor. But it's not a firm rule. Even ignoring Switzerland again (and some other landlocked but wealthy European countries), there's landlocked Botswana - one of Africa's richest states. And not being landlocked certainly doesn't automatically make you wealthy - e.g. Nigeria, again.
A view advanced in one of my geography A-level text books more than 30 years ago was climate: the debilitating heat of the tropics is not conducive to hard and productive labour - physical or mental. That sounds simplistic, almost laughable, but what about those surveys that tell employers here in the UK to keep their offices at exactly the right temperature to ensure happy and hard-working employees?
Tanzania's Julius Nyerere (a generally well-meaning fool) certainly thought climate was important. He said the extremes of summer and winter in the higher latitudes instilled a discipline in their inhabitants. It taught them to take good advantage of the summer to prepare for the winter ahead. In the tropics, such planning is not needed as much. Some food crops may grow all year round, there's no need to draught-proof your home against winter gales, the same clothes can be worn in all months.
I have two recommendations for escaping poverty: avoid violence and get a good government. There are no countries in the world that are violent and badly-run and rich.
My advice to DfID is - except in those cases where it may be possible to recolonise a violent, very badly run and very poor country to turn it around (what we are doing in Sierra Leone) - only invest your aid in countries that are peaceful and well governed. Otherwise, it will just go to waste.