The novel is set in early 19th century imperial England. The action takes place exclusively within the borders of England itself. The most direct descriptions of Jane's surroundings focus on quintessentially English weather and geography, such as fog and craggy landscapes. Brontë demonstrates some interest in domestic social issues, for instance by using Lowood to critique charity schools. But the novel is most invested in the social issues posed by England's position in a broader global context. Mr. Rochester is heavily implicated in the importation of corruption from outside England's borders, and the plot revolves around his and Jane's attempts to be free of that corruption.
In particular, the novel is concerned that England is being tainted with racial politics, colonial trade, and the slave labor that supports it. Frequent references to choppy waters (in Jane's watercolors, for example) evokes the fact that England is an island, and that its imperial expansion beyond its borders is a dangerous undertaking. Mr. Rochester's ill-fated marriage to Bertha, a Creole woman he meets through his family's business in the West Indies, functions within the novel as punishment for trying to make a fortune through colonialism. Bertha (who deserves better than she gets in the novel) is not only a burden to Mr. Rochester, but also a threat to Jane's happiness because her existence thwarts Jane's marriage to Mr. Rochester. Colonialism thus has a ripple effect on "innocent" people like Jane, who have never even left England.
Notably, the main concern the novel presents about colonialism is not the human rights of colonized and enslaved people, but rather the well-being of white English people like Jane, who accidentally suffer the consequences of their neighbors' imperial ventures. This concern is especially evident in Chapter 15, when Mr. Rochester tells Jane how Adèle came to live with him and reveals a cigar smoking habit:
[']I sat down, and took out a cigar – I will take one now, if you will excuse me.'
Here ensued a pause, filled up by the producing and lighting of a cigar; having placed it to his lips and breathed a trail of Havannah incense on the freezing and sunless air, he went on – [...]
The cigar smells like Havannah because that is its origin: it is proof that Mr. Rochester has brought a bit of an imperial colony back home. The cigar allows the novel to register colonialism as unnatural and threatening because the "Havannah incense" is incongruous with the "freezing and sunless air." The cigar represents the way colonialism is seeping into England's pure air, intermingling with its trademark fog and threatening its national identity. This cigar does not belong in England, and yet it has been brought here.
The novel is somewhat less troubled by St. John's missionary work in India, another colony where England was causing considerable harm. Nonetheless, Jane declines to go to India with St. John. Instead, she opts to remain in England and marry Mr. Rochester once he is free of Bertha, Thornfield, and his ties to the West Indies. Jane's decision has to do with her personal feelings for Mr. Rochester, but it might also be read as a defense of English isolationism.
