The Norwegian Army (Hæren) is the land warfare service branch of the Norwegian Armed Forces. The Army is the oldest of the Norwegian service branches, established as a modern military organization under the command of the King of Norway in 1628. The Army participated in various continental wars during the 17th, 18th, and 19th centuries as well, both in Norway and abroad, especially in World War II (1939–1945). It constitutes part of the Norwegian military contribution as a charter member of the North Atlantic Treaty Organization (NATO) since 1949. Torstenson WarNorway during the Great Northern War and Theatre War After the Kalmar War broke out in 1611, the Danish-Norwegian king, Christian IV tried to revive the leidang, with dire results. As the Norwegian peasantry had not been armed or trained in the use of arms for nearly three centuries, they were not able to fight. Soldiers deserted or were captured. The soldiers had to participate in military drills, while providing supplementary labor to the local community when not in active service. Although the army still did not represent the whole nation, as city residents were exempt from military duty, 1628 is generally regarded by historians as the year when the modern Norwegian army was born. As a result of the Torstenson war (Torstenssonfejden, Hannibalfeiden, Torstensonska kriget) lasting from 1643 to 1645, Danish–Norwegian territories were to be ceded to Sweden. This led Christian IV to invite German mercenaries to coach and command the Danish–Norwegian armed forces: a decision echoing down the centuries in traces of German vocabulary used by the Norwegian military to this day. In the early 18th century the Swedes invaded Norway again, and this time the Norwegian army held its own, setting the stage for nearly a century of peace – the longest yet in early modern and modern Norwegian history – during which time a distinct Norwegian identity began to evolve. German ceased to be the official language of command in the army in 1772, in favour of "Dano-Norwegian".