After the plebiscites in Zones 1 and 2, it was the task of the CIS to make suggestions concerning the definitive border between Denmark and Germany, taking account of commercial and geographical factors. Danes and Germans both tried to influence the work being done by the commission.

In the southern part of Zone 1, areas with  German majority were often geographically adjacent and partly borders on Zone 2. The Germans therefore suggested that the border should follow the co-called ‘Tiedje Line’.

This was a boundary line proposed by Johannes Tiedje, passing north of Højer, Tønder, Ravsted and Tinglev, and south of Gråsten to Flensburg Fjord.

Similarly, the Flensburg Movement tried to arouse interest in Denmark for the internationalisation of Zone 2 with its financial links to Denmark, with a new plebiscite to be held 10-15 years later, hoping thus to incorporate more areas (especially Flensburg) into Denmark.

Neither of these proposals was adopted by the Allies and the CIS. On 16 April 1920, therefore, the Commission ratified its own proposal for a new Danish-German border. This conclusion was not reached unanimously: a majority, with the Chairman having the casting vote, went in for the Clausen Line, which settled the border between Zones 1 and 2. A minority had wanted the border a little further south.

In Paris, the peace conference followed the majority proposal, and on 8 May, the Conference of Ambassadors accepted the Clausen Line. On 15 June, the Danish Ambassador, Bernhoft, received a note explaining where the border was to be drawn.

The new border was not just a line drawn on the map. It left national minorities on both sides and was a sharp dividing line between what was Danish and what was German in all areas – political, economic and social.

The German Foreign Ministry estimated that the German minority in North Schleswig encompassed  some 25-30,000 people, corresponding to a sixth of the population of North Schleswig.

By far the majority of them were living in thirty parishes and towns in the southernmost border area, which at the time was called ‘the crooked square’. From 1920, the German minority established an organisation with associations and institutions that could help preserve German identity.

While the German section of the population in North Schleswig had to get used to being a national minority, this was nothing new for the Danish minority in South Schleswig. What was new for these people was that they now had to stand on their own two legs, though they were heartened by the fact that Denmark had moved closer to them, physically and mentally.

The ‘Schleswig Association’ was founded as early as 26 June 1920. Its aim was to “… gather our countrymen together for mutual support in all matters relating to the people, to strengthen Danish culture, enlightenment and intellectual life, and for them to maintain lively connections with their countrymen north of the new Danish border”.

Even before the plebiscite was concluded, Germany urged Denmark to open two-part negotiations with a view to creating the same rights for both the Danish and German minorities.

However, the Danes were only interested in three-part talks about the legal position of minorities involving Denmark, Germany and the Allies. The German government could not accept this and therefore no common minority agreement was reached until 35 years later in 1955.