I had half forgotten about the World Bank and not really realised what it was there for. (Must remember to sack my secret UN connections forthwith.) Mind you, if michael is right about the World Bank's sucess rate...
Another example of a franchise system, or something pretty similar, was India/Pakistan/Bangladesh during the East India Company/British Raj era. The Brits didn't exactly colonise India (as it was at the time) in the conventional sense, rather they went in primarily to trade rather than to rule. While there, they took the country forward in leaps and bounds, developing the roads, railways and governing bureaurocracy necessary to help the ecomomy boom. When I was in India briefly a few years ago, I expected a lot more resentment toward the Brits, but in general most people seemed to think that the British Raj era had been a very good thing for the country (with the exception of the decision to split the country up to create Pakistan and Bangladesh, causing the upheaval of millions and death of many thousands).
I don't think it would be hard to find countries willing to sign up to a franchise model based on the UK, US, Japan, France, Germany, etc. There are dozens of countries in the world where the government is hardly fit to run a three-legged race, let alone a country with a solid economy and effective public services that make a country nice to live in.
I've argued about this with friends before, and one of the points that came up was that the people probably wouldn't want to lose their culture. Maybe not, but to what extent? If you were living in a post-Mugabe Zimbabwe, would preserving your culture in aspic really be your primary concern, or would you rather put food on your family's table, have schools to send your kids to, sanitation, reduced corruption, etc?
I think the key point I'm trying to get at is to think of countries in the same way that we think of companies. Around the world, across all industries, small companies are constantly being bought up by larger ones. In many cases, this benefits the employees of the smaller company, not just the owners. Take, for example, the makers of satellite mapping software Keyhole, or online word processing software Writely. Most people won't have heard of these companies, and I suspect if they had not been bought by Google and rebranded as Google Earth and Google Documents, they employees would still be toiling away in relative obscurity today. Instead they work on services used by millions of people, probably get paid a fair amount more plus various benefits, and can impress potential employers just by mentioning Google on their CVs.
Such I believe it could be for the residents of countries. If the Zimbabwes of this world became UK franchises, they would also benefit in similar ways.
Obviously I'm only suggesting this for cases where the people of the country positively wanted to enter into such a business arrangement. I'm not in any way suggesting that we should go out to invade anyone. As michael points out, we do get involved in 'nation building' after wars, but why stop there? I'd think there's a much, much higher chance of success in an already peaceful country.