again. By the early 1950s, it had nevertheless stabilised at a level four times higher than the pre-war number. In the Copenhagen-Bonn declaration of 1955, West Germany (later Germany as a whole) and Denmark promised to uphold the rights of each other's minority population. Today, both parts co-operate as a cross-border Euroregion: Region Sønderjylland–Schleswig. As Denmark and Germany are both part of the Schengen Area, there are no regular controls at the border. Dukes and rulers Name and naming dispute In the 19th century, there was a naming dispute concerning the use of or and (Southern Jutland). Originally the duchy was called but in the late 14th century the name of the city Slesvig (now Schleswig) started to be used for the whole territory. The term was hardly used between the 16th and 19th centuries, and in this period the name had no special political connotations. However, around 1830 some Danes started to re-introduce the archaic term to emphasize the area's history before its association with Holstein and its connection with the rest of Jutland. Its revival and widespread use in the 19th century therefore had a clear Danish nationalist connotation of laying a claim to the territory and objecting to the German claims. "Olsen's Map", published by the Danish cartographer Olsen in the 1830s, used this term, arousing a storm of protests by the duchy's German inhabitants. Even though many Danish nationalists, such as the National Liberal ideologue and agitator Orla Lehmann, used the name , it began to assume a clear German nationalist character in the mid 19th century – especially when included in the combined term "Schleswig-Holstein". A central element of the German nationalistic claim was the insistence on Schleswig and Holstein being a single, indivisible entity. Since Holstein was legally part of the German Confederation, and ethnically entirely German with no Danish population, use of that name implied that both provinces should belong to Germany and that their connection with Denmark should be weakened or altogether severed. After the German conquest in 1864, the term became increasingly dominant among the Danish population, even though most Danes still had no objection to the use of as such (it is etymologically of Danish origin) and many of them still used it themselves in its Danish version . An example is the founding of (The North Schleswig Farmers Association). In 1866 Schleswig and Holstein were legally merged into the