Niall Ferguson nicely summarizes the critiques of empire by dividing them between critiques that focus on the effect on subject peoples and critiques that focus on the effects on the subjectors.

The first critiques, which focus on the effects on the subject peoples, can take a nationalist or a Marxist form. As Ferguson puts it, “The central nationalist/Marxist assumption is, of course, that imperialism was economically exploitative: every facet of colonial rule, including even the apparently sincere efforts of Europeans to study and understand indigenous cultures, was at root designed to maximize the surplus value that could be extracted from the subject peoples.”

The second set of critiques, which he describes as “liberal” critiques, take the opposite tack:

“It is precisely because imperialism distorted market forces – using everything from military force to preferential tariffs to rig business sin favour of the metropolis – it was not in the way of long-term interests of the metropolitan economy either. In this view, it was free economic integration with the rest of the world that mattered, not the coercive integration of imperialism.” Domestic investment could have been better for the British economy, and would not have imposed the burden of maintaining the empire.

This critique is often joined to an evangelistic attachment to the benefits of commerce. William Cobden said that commerce was a “grand panacea” and “like a beneficent medical discovery, will serve to inoculate with the healthy and saving taste for civilization all the nations of the world. Not a bale of merchandise leaves our shores, but it bears the seeds of intelligence and fruitful thought to the members of some less enlightened community; not a merchant visits our seats of manufacturing industry, but he returns to his own country the missionary of freedom, peace, and good government – whilst our steamboats, that not visit every port of Europe, and our miraculous railroads, that are the talk of all nations, are the advertisements and vouchers for the value of our enlightened institutions.”