Question: What campaign by Sweden led to Denmark losing a third of its territory with the treaty of  Treaty of Roskilde?
Sentence (from "Treaty of Roskilde"): After a devastating defeat, Denmark-Norway was forced to give up a third of its territory to save the rest, the ceded lands comprising Blekinge, Bornholm, Bohuslän (Båhuslen), Scania (Skåne) and Trøndelag, as well as her claims to Halland.
Relevant evidence: Yes