What campaign by Sweden led to Denmark losing a third of its territory with the treaty of  Treaty of Roskilde?
Treaty of Roskilde The Treaty of Roskilde was concluded on 26 February (OS) or 8 March 1658 (NS) during the Second Northern War between Frederick III of Denmark–Norway and Charles X Gustav of Sweden in the Danish city 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.
War against Sigismund The war against Sigismund (Swedish: "Kriget mot Sigismund" ) was a war between Duke Charles, later King Charles IX and Sigismund, King of Sweden and Poland. Lasting from 1598 to 1599, it is also called War of Deposition against Sigismund, since the focus of the conflicts was the attempt to depose the latter from the throne of Sweden. The war eventually resulted in the deposition of Sigismund, with Duke Charles taking over the government and later also acceding to the throne.