In Wide Sargasso Sea, Rhys writes, "'Of course they have their own misfortunes. Still waiting for this compensation the English promised when the Emancipation Act was passed. Some will wait for a long time'" (Rhys 15). The socio-political framework for this novel is the Emancipation Act (1833), which caused turmoil and left feelings of animosity in its aftermath. This historical event, and the repercussions of it, sets the tension and chain of events that begin in the first part of the novel. Rhys moves the timeline of Jane Eyre up, meaning Bertha (Antoinette) is no longer a slave owner. Although there can only be speculation at the choice of moving the time of the novel, it is undeniable that it creates more sympathy for Bertha than if she was a slave owner. This increased sympathy for Bertha also leads to having more harsh feelings toward Rochester, as he is no longer leaving a "slave owner," but rather the daughter of a slave owner who inherited the abuse of what her mother did.
For further reading, investigate James McPherson’s article, “Was West Indian Emancipation a Success? The Abolitionist Argument during the American Civil War.” It gives background and debate on the successfulness of the Emancipation Act, told from the perspective of analysis of America's Emancipation (it discusses British Emancipation in the West Endies as an example to compare to).
Bibliography: McPherson, James. “Was West Indian Emancipation a Success? The Abolitionist Argument during the American Civil War.” Caribbean Studies, vol. 4, no. 2, 1964, pp. 28-34.
Rhys, Jean. Wide Sargasso Sea, W. W Norton & Company, 1966.