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 Paris (1810)"): This was followed in January 1812 by French occupation of Swedish Pomerania for violation of the Continental System, since Sweden was still trading with the UK, and, in April, Sweden's conclusion of the Treaty of Petersburg with Russia against France.
Relevant evidence: No