son and Denmark's future king, Eric of Pomerania forced the Schauenburgers to surrender the city of Flensburg to him. War broke out in 1410, and Eric conquered the islands of Als and Ærø. In 1411, Holstein-Rendsburg, which until 1403 had incorporated all Schauenburg lines except of Pinneberg, retook Flensburg, but in 1412 both sides agreed that an arbiter should settle the dispute, Ulrich I, Duke of Mecklenburg-Stargard. Ulrich awarded the city to Denmark, and Queen Margaret took possession of it. During her stay in Flensburg, she was struck by the plague and died shortly after. War returned and a new mediation attempt was undertaken in 1416 by the Hanseatic League. Both sides recognised the League as arbitrators and Denmark pledged the city of Schleswig as security; the Holstein-Rendsburg pledged the stronghold of Tönning, but the mediation attempts were in vain. In 1421, the Holsteiners succeeded in regaining the cities of Haderslev, Schleswig, and Tønder. The Emperor's verdict In 1422, both sides recognised Duke Henry X of Silesia (also known as duke Heinrich Rumpold), envoy of the Holy Roman Emperor, as arbitrator. He managed to persuade the Schauenburgers to call off a planned attack on Flensburg, but died on 18 January 1423 before reaching a verdict. His master, Emperor Sigismund, now wished to settle the issue, a decision strongly opposed by the Schauenburgers. He called upon Louis of Cattaneis from Verona to travel to the disputed province and investigate the case. A similar process took place in Denmark. The Assemblies of both Lund, Ringsted, and Ribe all reached the conclusion that Schleswig was governed by Danish laws and formed part of Denmark. The decision made by the Assembly of Ribe on 4 August 1421 is of particular interest, since both the bishops of Ribe and Schleswig, the abbots from the monasteries of Ryd (modern Glücksburg) and Løgum as well as councillors from Flensburg, Aabenraa, Haderslev, and Ribe were all present. The assembly ruled that Schleswig was part of Denmark with the following argument ... the (people) of Southern Jutland use Danish law and have kept it since it was given. Second, all the old rights granted upon the chapels and House of God in Schleswig, Ribe, and Haderslev were given by the kings of the Realm. Thirdly, every man knows where the borders are located, that Denmark and Holstein are separated; even the language in Southern Jutland is Danish to this