title of Duke of Schleswig was inherited in 1460 by the hereditary kings of Norway, who were also regularly elected kings of Denmark simultaneously, and their sons (unlike Denmark, which was not hereditary). This was an anomaly – a king holding a ducal title of which he as king was the fount and liege lord. The title and anomaly survived presumably because it was already co-regally held by the king's sons. Between 1544 and 1713/20, the ducal reign had become a condominium, with the royal House of Oldenburg and its cadet branch House of Holstein-Gottorp jointly holding the stake. A third branch in the condominium, the short-lived House of Haderslev, was already extinct in 1580 by the time of John the Elder. Following the Protestant Reformation, when Latin was replaced as the medium of church service by the vernacular languages, the diocese of Schleswig was divided and an autonomous archdeaconry of Haderslev created. On the west coast, the Danish diocese of Ribe ended about 5 km (3 mi) north of the present border. This created a new cultural dividing line in the duchy because German was used for church services and teaching in the diocese of Schleswig and Danish was used in the diocese of Ribe and the archdeaconry of Haderslev. This line corresponds remarkably closely with the present border. In the 17th century, a series of wars between Denmark and Sweden—which Denmark lost—devastated the region economically. However, the nobility responded with a new agricultural system that restored prosperity. In the period 1600 to 1800 the region experienced the growth of manorialism of the sort common in the rye-growing regions of eastern Germany. The manors were large holdings with the work done by feudal peasant farmers. They specialized in high quality dairy products. Feudal lordship was combined with technical modernization, and the distinction between unfree labour and paid work was often vague. The feudal system was gradually abolished in the late 18th century, starting with the crown lands in 1765 and later the estates of the nobility. In 1805 all serfdom was abolished and land tenure reforms allowed former peasants to own their own farms. 19th century and the two Schleswig wars From around 1800 to 1840, the Danish-speaking population on the Angeln peninsula between Schleswig and Flensburg began to switch to Low German and in the same period many North Frisians also switched to Low German. This linguistic change