Denmark remained neutral during World War I, but the conflict affected the country to a considerable extent. As its economy was heavily based on exports, the unrestricted German submarine warfare was a serious problem. Denmark had no choice but to sell many of its exports to Germany instead of overseas nations. Widespread profiteering took place, but commerce also suffered great disruption because of the conflict and because of the ensuing financial instability in Europe. Rationing was instituted, and there were food and fuel shortages. In addition, Denmark was forced by Berlin to mine the Sound to prevent British ships from entering it. Following the defeat of Germany in the war (1918), the Treaty of Versailles (1919) mandated the Schleswig Plebiscites, which resulted in the return of Northern Schleswig ( South Jutland) to Denmark. The king and parts of the opposition grumbled that Prime Minister Carl Theodor Zahle (in office 1909–1910 and 1913–1920) did not use Germany's defeat to take back a bigger portion of the province, which Denmark had lost in the Second Schleswig War in 1864. The king and the opposition wanted to take over the city of Flensburg, while the cabinet insisted on only claiming areas where a majority of Danes lived, which led to a plebiscite in the affected areas over whether they wanted to become a part of Denmark or remain within Germany. Believing that he had the support of the people, King Christian X used his reserve power to dismiss Zahle's cabinet, sparking the Easter Crisis of 1920. As a result of the Easter Crisis, the king promised to no longer interfere in politics. Although the Danish Constitution was not amended at that time, Danish monarchs have stayed out of politics since then. The end of the war also prompted the Danish government to finish negotiating with Iceland, resulting in Iceland becoming a sovereign Kingdom on 1 December 1918 while retaining the Danish monarch as head of state.
