During the first nine years of Frederick's reign the country had peace; but the war which then broke out was most fatal in its result. The Swedish king, Charles X. Gustavus, was at war with Poland, and rumor had it that he had suffered serious defeats. Although the country highly needed peace, the army and navy, as well as the finances, being in a miserable condition, King Frederick believed there was an opportunity to recover the lost provinces, and war against Sweden was declared, 1657. But King Charles hastily left Poland and invaded Denmark, and, before the year was closed, he had conquered Holstein, Schleswig and Jutland. The winter being unusually severe, he could march across the ice to the islands of Langeland, Lolland, and Falster, and, in February, he stood with his whole army in Zealand (Sjælland) and threatened Copenhagen. King Frederick was obliged to sign the peace at Roskilde (February 26, 1658), by which he ceded to Sweden the Norwegian provinces of Bahus-Len and Throndhjem Stift and the Danish provinces of Scania, Halland, Blekinge, and the island of Bornholm. Thus Norway was again deprived of some territory, although the Norwegians, under Iver Krabbe (after whom the war was called the Krabbe War), had repulsed the attacks of the Swedes, while General Jorgen Bjelke had conquered Jemteland, which, however, had to be evacuated when peace was concluded. Having discovered the great weakness of Denmark, King Charles thought he saw a chance to place the three crowns on his head, and five months later he broke the peace, under some pretext, and again landed with a well-equipped army, with which he besieged Copenhagen. He captured the castle of Kronborg and other points of defence, and arrogantly declared, to the Danish messengers sent to him, that "it could matter little whether the king of the Danes was called Charles or Frederick, and that he would explain the causes of the war after Denmark had been taken." At Copenhagen, however, King Charles met a stronger resistance than he had expected. A Dutch fleet, under Admiral Opdam, succeeded in forcing its way past Kronborg and the Swedish fleet, and brought provisions and help to the starving citizens. When Charles, during the night of February 10, 1659, tried to take the city by assault, he was repulsed after a desperate conflict, leaving 2,000 dead and wounded in the hands of the Danes. Later in the year King Frederick succeeded in securing the assistance of France, England and Holland. After a conference held at the Hague, a Dutch fleet, under Admiral de Ruyter, was sent to aid the Danes, and in November, 1659, the Swedish army was defeated at Nyborg.