Dodecanese relative quiet and prosperity. In 408 BC, the three cities of Rhodes had united to form one state, which built a new capital on the northern end of the island, also named "Rhodes"; this united Rhodes was to dominate the region for the coming millennia. Other islands in the Dodecanese also developed into significant economic and cultural centers; most notably, Kos served as the site of the school of medicine founded by Hippocrates. However, the Peloponnesian War had so weakened the entire Greek civilization's military strength that it lay open to invasion. In 357 BC, the islands were conquered by
Dodecanese territories, occupied all the present-day Dodecanese except for Kastellorizo. After the end of the war according to the Treaty of Ouchy, Italy maintained the occupation of the islands as guarantee for the execution of the treaty. The occupation continued after Italy declared war on the Ottoman Empire (21 August 1915) during the First World War. During the war, the islands became an important naval base for Britain and France; Italy was allied with both nations during World War I. The Dodecanese were used as a staging area for numerous campaigns, most famously the one at Gallipoli. Some of the smaller