Balkan Peninsula, peninsula in south-eastern Europe, bounded on the east by the Black Sea and the Aegean Sea, on the south by the Mediterranean Sea, and on the west by the Adriatic and Ionian seas. It has always been strategically important as part of the land bridge between Europe and Asia and as the overland route from the Mediterranean to the Black Sea. The Balkan Peninsula generally encompasses the countries that are commonly known as the Balkan states: Croatia, Bosnia and Herzegovina, the Former Yugoslav Republic of Macedonia, Serbia and Montenegro, Albania, continental Greece, and Bulgaria. Slovenia and Romania are also sometimes included in this designation. In addition, the south-eastern part of the peninsula includes Eastern Thrace, the European part of Turkey. Geographically, the northern boundary can be defined by the River Sava; the lower River Danube from the point, at Belgrade in Serbia, where the Sava joins it; and a line drawn arbitrarily from the upper Sava to the Adriatic Sea near Rijeka, Croatia. This northern boundary encompasses a region that (together with Romania, but excluding Montenegro, Dalmatia, and the Ionian Islands) constituted most of the European territory of the Ottoman Empire from the late 15th to the 19th century.
The Balkan Peninsula is a region of great geographical diversity—from the flat plains of the Danube to the forest-covered Rila Mountains and the barren regions of karst. Most of the region is mountainous—Balkan means “mountain” in Turkish—with streams flowing in every direction. The drainage basin of the Danube is the most important hydrographic feature. From the southern slopes of the Rhodope Mountains, the River Vardar flows into the Aegean Sea; and, at the most westerly point of the Balkan Mountains, the Morava flows into the Danube. The Balkan Mountains form the largest continuous range; other mountainous sections are the so-called Dinaric Alps along the Adriatic coast, the Carpathian Mountains, which rise in Romania, the Rhodope chain between the Former Yugoslav Republic of Macedonia and the Maritsa Valley, the Pindus Mountains in north-western Greece, and isolated summits of historical importance, including Mounts Olympus, Pelion, and Óssa in Greece. Lake Scutari, on the Montenegro-Albania border, and Lake Ohrid, on the border between Albania and the Former Yugoslav Republic of Macedonia, are the only lakes of importance on the peninsula. The southern part of the peninsula, which forms the mainland of Greece, has a mild Mediterranean climate, but the rest of the region is subject to the severe winters and hot summers of south-central Europe. The north-western portion has few lowlands and is characterized by unbroken, jagged hills; the southern portion has much more level terrain.
Balkan history is characterized by military and political strife. Conflicts among the Balkan peoples and nations have been common, and the Balkans have played a key role in European power struggles. The region has been inhabited since c. 200,000 bc. By 7000 bc a distinctive Stone Age culture had evolved. The peninsula was settled, in 3500 bc, by semi-nomadic farmers from the Russian steppes, and later still by Celts in the Bronze Age. The Slavs appeared around the 3rd century and migrated to the peninsula in large numbers in the 6th century, and Bulgar tribes appeared in the 7th century; eventually the Bulgars were assimilated by the Slavs. Slavic, Magyar, and Germanic settlers evolved in comparative isolation because of the natural barriers to communication within the peninsula, each group developing its own local variant of religion, language, and customs. All suffered periodic persecution by the Turks. During the Byzantine era, a form of Orthodox Christianity was established in parts of the Balkans, while Islam spread in those regions held by the Turks. From the late Middle Ages onward, the Ottoman Turks gradually took control of almost the entire peninsula. However, the balance of power in the Balkans changed once again after the siege of Vienna (1683) when the Ottoman Turks were driven back by the Austrian Habsburgs and by Russia, both of which powers sought access to the seas surrounding the peninsula. Intra-Balkan conflict remained historically endemic, and the Balkans continued to play a key role in European power struggles.
In the 19th century, one Balkan nation after another developed strong nationalist movements, forcing Turkey to concede a degree of autonomy to each nation. The Balkan League of 1912 was formed to counter Turkish rule in the area, leading to the Balkan Wars. Two years later Pan-Slavism contributed to the outbreak of World War I when the heir presumptive to the Austrian emperor was assassinated at Sarajevo by a young Serbian nationalist, Gavril Princip.
After World War I ended in 1918 and the Ottoman Empire was dismantled, Bosnia and Herzegovina, the provinces of Croatia, Slavonia, and Carniola united with Serbia and Montenegro to form the Kingdom of the Serbs, Croats, and Slovenes, later named Yugoslavia. As a consequence of the Balkan Wars and World War I, European Turkey had for all practical purposes ceased to exist.
Between the two world wars, political leaders tried to prevent the Balkan countries from again becoming the “powder keg of Europe”. The Balkan Pact of 1934 sought to unify the countries by a non-aggression pact and guarantees of the Balkan frontiers. It was signed by Yugoslavia, Turkey, Greece, and Romania, but the international friction and open rifts that preceded World War II were not lessened. Greece, like Turkey, resisted the infiltration of the Axis powers, but the influence of fascist Italy and Nazi Germany was strong in the other Balkan countries. In April 1939 Italy seized Albania. In October 1940, one year after the outbreak of World War II, Italy invaded Greece but was thrown back into Albania, while the Germans swept through Romania and Bulgaria. Yugoslavia and Greece fell to the Germans early in 1941, despite well-organized guerrilla resistance that continued throughout the war. Bulgaria and Romania officially joined the Axis, but Yugoslavia and Greece established Allied governments-in-exile, which were replaced at the end of the war by provisional governments and finally by the kingdom of Greece and the republic of Yugoslavia. Albanian resistance forces set up a provisional government that gained control after German withdrawal from the Balkans and proclaimed the country the People's Republic of Albania. Upon the defeat of the Axis, a republic was also established in Bulgaria.
A second Balkan Pact between Yugoslavia, Greece, and Turkey was concluded in 1954 and provided for common military assistance in the face of aggression. After the collapse of Communism in 1991, four Yugoslav republics—Slovenia, Croatia, Bosnia and Herzogovina, and Macedonia—declared their independence from Yugoslavia, and full-scale civil war erupted. Serbia and Montenegro became separate countries, though the latter's government has not been internationally recognized.