I think that it would be fragment but I am not sure.
The clause <em>when we can rest </em>is a subordinate/dependent clause, meaning that it cannot stand on its own - it has to be a part of a larger, independent clause, as is the case here.
Answer:
A Vindication of the Rights of Woman is a straight-up philosophical treatise, one that Wollstonecraft wrote for a single central purpose: to show the world that women should be entitled to the same civil rights as men
Explanation:
No change! this sentence is correct!
