Its demarcated land frontiers were settled by treaty early in the twentieth century and have since remained stable. The boundary with Greece was confirmed by the Treaty of Lausanne (1923), which resolved persistent boundary and territorial claims involving areas in Thrace and provided for a population exchange (see: War of Independence). Under the agreement, most members of the sizable Greek-speaking community of western Turkey were forced to resettle in Greece, while the majority of the Turkish-speaking residents of Thrace who were not forced out during the Balkan wars were removed to Turkey. The boundary with Bulgaria was confirmed by the Treaty of Lausanne (1923). Since 1991 the more than boundary with the former Soviet Union, which was defined in the 1921 Treaty of Moscow (1921) and Treaty of Kars, has formed Turkey's borders with the independent countries of Armenia, Azerbaijan, and Georgia. The boundary with Iran was confirmed by the Treaty of Kasr-ı Şirin in 1639. The boundary with Iraq was confirmed by the "Treaty of Angora" (Ankara) in 1926. Turkey's two southern neighbors, Iraq and Syria, had been part of the Ottoman Empire up to 1918. According to the terms of the Treaty of Lausanne (1923), Turkey ceded all its claims to these two countries, which had been organized as League of Nations mandates under the governing responsibility of Britain and France, respectively. Turkey and Britain agreed the boundary in the Treaty of Angora (Ankara). Turkey's boundary with Syria has not been accepted by Syria. As a result of the Treaty of Lausanne, the former Ottoman Sanjak (province) of Alexandretta (present-day Hatay Province) was ceded to the French which administered it on behalf of the League of Nations. However, in June 1939 the people of Hatay had formed a new independent State and immediately after, the parliament voted to unite with Turkey. Since achieving independence in 1946, Syria has harbored a lingering resentment and this issue has continued to be an irritant in Syrian-Turkish relations. The 1st Geography Congress, held in Ankara City between 6–21 June 1941, divided Turkey into seven regions after long discussions and work. These geographical regions were separated according to their climate, location, flora and fauna, human habitat, agricultural diversities, transportation, topography, etc. At the end, 4 coastal regions and 3 inner regions were named according to their proximity to the four seas surrounding Turkey, and their positions in Anatolia.