It is hard to ignore the way in which this text relates so closely to the colonial expansionism that had brought the powers of Europe into contact with "brave, new worlds" that had just been "discovered." Historically, these new relationships gave European powers the opportunity to exploit and disempower natives, and it is hard not to see a parallel situation in both Prospero's relationship with Caliban and with Ariel. While most considered that Europeans had a "god-given" right to the colonial power they were beginning to wield, there were a few dissenting voices that suggested that the "civilisation" that the European powers were supposedy bringing to these oppressd colonies might not be the most beneficial thing for them.
The relationship between Prospero and Caliban is therefore of particular interest with regard to this question of colonialism. He is shown to be enslaved, maltreated and abused by people who cold-heartedly use him for their own benefits. Yet at the same time, Caliban himself is shown to be a treacherous character who deliberately tried to rape Miranda and make her bear his children. He laments his lack of success in this regard:
Thou didst prevent me; I had peopled else
This isle with Calibans.
He willingly tries to betray Prospero in a laughable attempt by finding a new master in Stephano. Having been taught the language of his oppressors, he now seeks to use that to overthrow Prospero. In him, therefore, Shakespeare seems to present a very problematic depiction of colonialism. Was Prospero right to enslave him? Was he right to "civilise" him? Does this process make Caliban happier? These are questions with no easy answers, but ones that reflect the different approaches to colonialism in Shakespeare's day.