Magwitch’s situation is an example of imperialism because when he is arrested he is sent to Australia. Australia was a British colony where many prisoners were sent. Once there, Magwitch was able to make enough money to send back to England to turn Pip into a gentleman.
Transporting prisoners was a common way of dealing with England's worst criminals. Convicts were routinely taken to the British colonies in America until the Revolutionary War, and after that, to Australia and Tasmania. (enotes etext Reading Pointers for Sharper Insights, p. 4)
Pip is distantly aware of the fact that Magwitch, his convict, has been transported. In those days it was a life sentence, and to return meant death for Magwitch. Magwitch being transported to Australia is a comfort to Pip, but he still feels sorry for him.
My comfort was, that it happened a long time ago, and that he had doubtless been transported a long way off, and that he was dead to me, and might be veritably dead into the bargain. (ch 19, p. 103)
In Australia, Magwitch is able to make a good deal of money. Of course, all of his money goes to Pip. Yet it is an example of how a person could make a new life in a new land.
“I've been a sheep-farmer, stock-breeder, other trades besides, away in the new world,” said he: “many a thousand mile of stormy water off from this.” (ch 39, p. 215)
Magwitch is proof that not every criminal that was transported was evil. Some of them might have just needed a second chance. If they came back to England, they were hanged.