Colonialism and Growth
During the forty year period 1950-1990 world population grew at an annual rate of just under 2%, and total production of goods and services grew at 4% per year. This means that production per person grew at more than 2%, implying that income per person more than doubled over these years. These figures refer to the entire world, rich and poor alike. Nothing remotely like this has ever been seen before.
For comparison, during the 18th century world population and production both grew at about 0.33% per year, and average living standards grew not at all. From 1800 to 1950, when the industrial revolution began to transform the lives of large numbers of people, population grew at 0.7% and production at 1.4%, implying per capita income growth of 0.7%. (All of these figures are taken from Tables 5.1 and 5.2 of Lectures on Economic Growth.)
The figure below plots the course of per capita incomes in five parts of the world since 1750. Groups I, III, and IV are countries largely populated and ruled by Europeans, wherever located, ordered from most to least successful economically. Group II is Japan. 
The final curve includes all of Africa and Asia (except for Japan): today, more than two-thirds of the world’s population. British India and Africa are here, along with the subjects of French, Dutch, German, Portuguese, Spanish, and American imperialism. So is China, with its ambiguous role in the colonial age, and those few others that somehow remained outside the empires of Europe and Japan. The striking fact is that these colonial subjects had the same living standards at the end of the colonial period as they had had two centuries earlier.
The British Empire shows up in this figure in two places. British-ruled and largely British-occupied Canada, Australia and New Zealand are included in the top curve, along with the US and the UK. The British-ruled and largely non-British occupied colonies of Africa and Asia are included in the bottom curve.
Showing the British colonies in Africa and Asia separately would have added no information: The pre-1950 histories of the economies in these parts of the world all show living standards that are roughly constant at perhaps $100 or $200 above subsistence levels. There are no differences in this regard between colonies and independent nations in this group (Japan, of course, excepted) or between the subjects of any one of the European empires or another. There is no reason to think that British or other imperialism caused the economic stagnation shown on the figure: Stagnation at income levels slightly above subsistence is the state of traditional agricultural societies anywhere and any time. But neither did the modern imperialisms alter or improve incomes for more than small elites and some European settlers and administrators.
The income curve for Africa and Asia turns up a bit after 1950. This may not look like much in the picture but it amounted to more than a tripling of incomes. The fact that living standards for masses of people in these populous, poor societies finally began to grow after independence is what made possible the high world-wide growth rates quoted at the beginning of these comments. The main economic event of the late 20th century was this diffusion of the industrial revolution to non-European societies, begun in Japan half a century earlier. A central question is why it did not begin much earlier, during the colonial period, at the same time that the industrial revolution was spreading throughout Europe.
That it did not do so is especially surprising and puzzling in view of fact that there were large-scale increases in the volume of world trade in the 19th century and considerable investment by the British in the Americas, India, and elsewhere. The security of foreign investment is an advantage of imperialism: British military power made Indian railroad bonds as safe for British savers as home investments were. India was surely better off with the British-built railroads than without them, but investments like these did not lead to anything like the kind of economic development we have seen in the post-colonial period.
The second, post-colonial phase of globalization has been associated with unprecedented growth in the living standards of hundreds of millions of people while the first, colonial phase was not.