At the end of the Italo-Turkish War of 1911-1912, the Italians captured the island of Kos , May 20, 1912, as most of the islands of the Dodecanese . The people of Kos, Greece 94%, first welcomed as liberators Italians, after 390 years of Ottoman occupation , hoping their independence or annexation of their island to Greece.
It was indeed planned by the Treaty of Ouchy on 18 October 1912, that Italy cede the Dodecanese to Turkey. But because of the First World War, the Italians consolidated their domination over the Dodecanese, the annexation was formalized by the Treaty of Lausanne of 1923 which Turkey renounced claim the Dodecanese. Islanders became Italian citizens, although one particular citizenship. Kos became vice-governor under the jurisdiction of Rhodes .
During the period from 1923 to 1943, the fascist government implemented an extensive program of "italianisation" with important interventions in education, religious issues, and the economy. Italians imposed an effective system of administration and undertook large public works to improve the infrastructure neglected by the Ottomans.
In 1933, an earthquake destroyed most of the buildings were rebuilt by the Italians.
Italian domination of Kos ended after the Italian surrender. In September 1943, the British tried to seize the island, but their troops were defeated by the German troops who had attacked against, Oct. 3, 1943 as part of Operation Polar Bear (Unternehmen Eisbär) 1388 British and 3145 Italian soldiers were captured hundreds of Italian officers who had turned against their former German allies were shot in what is known as the "Massacre of Kos." The island remained under German occupation until 1945. After the surrender of Germany May 9, 1945, Kos became a British protectorate for two years, then entered - as the entire Dodecanese - Greece into the fold in 1947. The official celebration of the reunification of the island with Greece took place on 7 March 1948.