So no, it's not colonialism.
It has to be something less visible. Something that a country like Afghanistan for example severely lacks.
You might point to dictatorships, but I would point to South and North Koreas.
South Korea was ruled by a brutal dictatorship for decades, in a way not so different from Egypt today. Yet that did not stop it from developing.
Even North Korea fares a lot better than many third world countries that have little to no enmities with their neighbors. I suspect the only reason North Korea sucks is because of the pressures/blockades imposed on it by the US (mostly for historical reasons).
China has been the richest and most powerful countries in the world for 2000 years before European nations crippled it in the Opium Wars.
Finland was never a colonial power, by the way. Sweden was, but Finland was still largely tribal a bit over a century ago, and was kind of a colony of Sweden and Russia alternately. The rise of Finland to one of the most civilised countries in the world over the period of a century is really interesting.
I fear racism is also a big factor. White people in Finland are more likely to get a break from other white people than black people in Ethiopia are.
But culture is also a big factor. In Europe, the most powerful economies are in the traditionally protestant north, whereas the Catholic south tends to have somewhat weaker economies. But why? And why were Muslim countries rich, powerful and advanced in the Middle Ages, and now not anymore?
> Finland was never a colonial power, by the way.
That was the whole sarcastically made point of the grandparent comment. Rich non-colonizing states vs. poor non-colonized states.
Colonisation obviously does play a role. It's ridiculous to claim that pillaging or oppressing another country doesn't hurt it, nor enrich the country that takes the profits. But it's not remotely the only factor at play. And the further in the past some events are, the more they get overshadowed by more recent history. I don't think Italy has much remaining benefit from the slaves the Roman Empire took from the Kelts they conquered.
The impact of colonialism is studied
under the institutionalist approach
to growth theory
authors being Acemoglu and Robinson.
The submission doesn't elaborate on it,
but the literature is out there.
Growth theory, or rather development economics, studies how and why wealth grows. And here go ... pretty much any economic growth models. I really don't know how else to say it.
Finally, an institutional approach to development economics studies how institutions might cause nations either grow or not, depending on their institutions, and the guys who kick-started this approach were Daron Acemoglu of MIT and James Robinson, of Chicago University. They have a book on it called "Why Nations Fail", released in 2012, which has already been recommended by another commenter. Their main thesis being that certain patterns of colonialism induce certain patterns of institutions, which they call "extractive", by which a minority appropriates most of a country's wealth for itself, while setting the country on a low growth path. The classic example being a resource-based economy under either a minority or authoritarian rule.
If this all sounds really general, that's because it is. I haven't read much on institutional economics, much less on the economics of colonialism. But I know it's out there.