The great triangle of the Balkan peninsula covers about 500,000sq.km and is mostly mountainous, split into many lands with varying relief, soil, climate, vegetation and animals, and therefore varying ways of human habitat. Balkans' natural extension is Asia Minor, with which it constitutes the platform between Europe and Asia. Hence the capital role of Bosphorus and Dardanelles, through which runs the seafaring route linking the Mediterranean with the Black Sea. Balkan lands' location in relatively open space and actually lesser access to the seas caused, that the peninsula for millennia has been a battleground of expansion and rivalry of various outer powers. In the ancient times Balkans were conquered by the Rome. Its descendant, the Byzantine Empire, for several centuries tried to hold the peninsula in its possession, although the migrations of nations, and particularly the settlement of the Slavic tribes, changed its ethnic composition and created basis for the establishment of new independent realms.

The shaky Greco-Slavic balance was destroyed in 14th and 15th centuries by the invasion of the Turkish Ottoman Empire, which at the peak of its conquests encompassed almost the whole area. Several centuries of the Turkish rule brought catastrophic consequences: wars, spread of Islam, cultural deformation, and economical and civilizational underdevelopment. Since the battle of Vienna (1683) the area of Turkey's rule shrunk as it had been driven back by the Austrians, Russians and indigenous liberation movements. But it was not until 230 years later that it was limited in 1912 to a scrap of the European continent (East Thrace) by the effort of the Balkan nations themselves. However, new independent states - Romania, Bulgaria, Serbia, Montenegro, Albania and Greece - emerged from the First Balkan War against Turkey antagonized and promptly started hostilities among themselves. The year 1913 brought a major fratricidal conflict, the Second Balkan War, in which the Bulgarians were defeated by allied Serbs, Greeks and Romanians, and which shaped divisions among Balkan peoples. Divisions even deepened and strengthened during the First World War.

In 1914-1918 Serbia and Montenegro, then Greece, and finally Romania were involved in war alongside the Entente, whereas Turkey and Bulgaria allied with the Central Powers. Formally neutral Albania was ravaged by both sides of the conflict. Bulgaria, defeated once again, ultimately lost her access to the Aegean Sea. Turkey, also defeated, faced a total disaster. She was saved by the democratic revolution and reforms carried out by Mustafa Kemal (Atatürk), discords among Entente powers, help from Soviet Russia and victory in war with Greece. Greece desired to restore the Byzantine Empire by reconquest of Asia Minor (1919-1922). This attempt resulted in Greek army's defeat in the battle on the Sakarya River (1921) and a catastrophe to the Hellenic population, which had to abandon Asia Minor after having lived there over 3000 years.

Inter-war relations in the Balkan Peninsula were shaped by the Versailles treaty. Serbia, Montenegro and southern Slavic lands of the former Austro-Hungarian monarchy made a new country - the Kingdom of Serbs, Croats and Slovenes (since 1929 - Yugoslavia), which together with Romania and Greece was interested in keeping its possessions. With time also Turkey joined them. This alliance became formal on 9 February 1934 when the four countries signed in Athens a political pact, so-called Balkan Entente. The pact foresaw mutual assistance of the parties in case of an aggression of a third Balkan country - presumably Bulgaria. Moreover Yugoslavia, Romania and Czechoslovakia created so-called Little Entente to protect themselves from Hungarian expansionism. Those pacts, which were supposed to preserve Versailles political status quo, constituted important links in the chain of France's alliances. The Munich policy had ruined the Balkan security system. It increased instability through Italian occupation of Albania and annexation of Austria and Czechoslovakia by Germany, which therefore reached the outskirts of the Balkans. She also increased her economic penetration of the region, which had been gradually transformed into a III Reich's supply subsidiary. Democracies' counteraction was weak. It did not halt German economic expansion, and guarantees accepted by Greece and Romania in spring 1939 brought a doubtful political effect. Only Turkey, afraid of Italian expansionism, after long negotiations signed on 19 October 1939 a mutual assistance treaty with France and Great Britain. The outbreak of the Second World War, and particularly France's and Great Britain's failure to fulfil their liabilities towards allied Poland, caused dismay in those political circles, which sought closer co-operation with the West. Balkan governments were waiting for the outcome of the contest in the western front; some of them desired territorial acquisitions, others wanted to defend their possessions, but all of them felt helpless in face of the powers' strength.

Balkan countries represent a substantial manpower and possess valuable natural resources. But their pre-war economic development was poor and could not provide adequate armaments and supplies to the armed forces. Economy was dominated by primitive agriculture. Peasantry constituted more than the half of the population. For centuries of hard toil they had been reclaiming plough soil from rocks and marshes but the level of agricultural production remained low. Grain production, but Greece, barely covered domestic demand, and only Bulgaria had grain surplus for export. Substantial portion in export made other agricultural products like tobacco, fruits, olives and wine. Knowledge and exploration of mineral resources were inadequate. Yugoslavia mined copper, Greece - nickel, but the ores were exported raw or semi-raw. Food processing and textile industries were better developed, while steel production was virtually non-existent. In 1937 the whole area had produced 320,000t of steel; almost entirely in Yugoslavia. The total production of electrical energy in 1938 barely approached 3 billion kWh. Communication grid was also inadequate and on top of that the mountainous terrain caused additional problems. Both roads and railways had a lot of bridges and tunnels, what augmented the danger of their total paralysis in case of air raids. Some areas were deprived of railways at all. Therefore the motor communication played important role both in passenger and cargo transportation. However merely first steps were made towards its development. Sea communication was important only in Greece.

Political relations in the Balkans were troubled by religious differentiation. Catholicism dominates in western Yugoslavia and northern Albania, other lands are Orthodox Christian. Islamic pockets were scattered throughout the whole region. Protestantism was present too, but without major influence. The ethnic mosaic is even more colourful; generally speaking all the countries are multinational to some extent. Yugoslavia is basically comprised by three nations - Serbs, Croats and Slovenes, as well as a number of minorities like Macedonians, Bulgarians and Russians, Albanians, Greeks and Turks, Germans, Italians, Hungarians and Romanians, Jews and Gypsies. It must be mentioned, though without hazarding into thorough and detailed examination that among Balkan peoples existed numerous prejudices, tensions and conflicts well rooted in the past centuries of coexistence and mutual hostilities. Some nations pursued domination over their neighbours, other sought emancipation, and both streams made a fertile soil for all kinds of extremism, especially nationalism, chauvinism and fascism. The only political power capable to raise over ethnic quarrels were communists. Banned and persecuted in all the countries, only they advocated the perspective of sensible modus vivendi. However, they were often referred to as a tool in the hands of the Comintern, it means - the foreign policy of the USSR. It actually came true after massive purges perpetrated by Joseph Stalin in 1937-1938, which left the communist movement weak and disorganized. Moreover, many people tended to see in the non-aggression treaty between the USSR and Germany (23 August 1939) a kind of alliance between Moscow and Berlin. This tendency left many communists and their sympathizers disoriented and disappointed.

Substantial role in establishing and maintaining dictatorships played military. Armed forces were dominated by manpower, for which there was not enough weapon and equipment. Troops were equipped and trained for fight with similar enemies and were no match to the armies, which represented European standard. Balkan countries' main combat force were land troops. Air forces and navy (but Greece) were auxiliary services. During the peacetime land forces were substantially expanded. In case of mobilization they would transform into infantry with average quantity of field and mountain artillery. Heavy, anti-tank and anti-aircraft artillery were inadequate. Tank troops were virtually nonexistent, motorization made just first steps and transportation mostly sustained on horses, mules and even oxen. It was not until late 1930's that air forces attracted more strategists' attention and possessed mostly obsolete planes. Only the Greek navy had considerable combat value. General conscription provided cannon meat, military careers were reserved for upper classes. A deep social gap divided ranks and files from commanding officers.

Such were briefly economic sources of interest in the Balkans on the part of German concerns as well as Adolf Hitler and his war economic advisers. But in Hitler's eyes Balkan peninsula also had a strategic importance. The bigger the longer Great Britain continued the war and gradually took over the strategic initiative in the Mediterranean - especially in its eastern part. In those circumstances subordination of the Balkans became the capital condition for the German land forces and Luftwaffe to get to the Rome-Berlin Axis' vulnerable Mediterranean theatre. The main reason of Hitler's interest in the Balkans came out from Barbaroßa - the plan to attack the USSR ripening since early autumn 1940. Therefore, through the economic and political pressure, at times balancing at the edge of black mail, Hitler - often supported but even more often surprised by his Italian allies - started the first stage of the conquest of the Balkans. Originally the Germans quite carefully strengthened their influence in Hungary and Romania. But in July 1940 it came to a serious conflict between the two countries. For Hungary spelled out her claims to Transylvania. Germany and Italy had to take a position in the conflict. In August, by the decision of so-called Vienna Award, they imposed on conflicting parties the solution, which served their own interests: they gave a large portion of the northern Transylvania to Hungary and the southern part of Dobruja to Bulgaria. They also approved the USSR's incorporation of Bessarabia, since 1918 under Romanian occupation. Those were major territorial losses, which agitated Romania. King Charles II had to step out in favour to his son Michael. To the prime-minister was assigned General Ion Antonescu, who opened the way to the fascist régime, and in foreign affairs closely collaborated with Hitler. Soon, under the guise of training the Romanian army, the Germans deployed their troops in Romania and gained valuable initial positions for invasion on the USSR.

Germans' penetration of Hungary and Bulgaria was carried out slower and more cautiously. Nevertheless they gradually created there a solid strategic rear for the war with the Soviet Union. This cautious, long-term policy was however disturbed in autumn 1940 by Italy's attack on Greece. The Greeks' resistance to the Italian invasion and their further successes in Albania caused German intervention and occupation of the Balkans. For the relatively low price (10,000 dead) the Germans had seized the whole south-eastern Europe and seriously menaced British positions in the Middle East as well as Soviet positions in the Black Sea. They had also secured possibility of unlimited exploitation of Balkan resources. This success, achieved within a short time and widely advertised by Göbbels' propaganda, had to confirm the myth of the invincible German Wehrmacht. In fact it was a victory over weak opponents, who on top of that failed to co-operate and were internally undermined. To Yugoslavia and Greece the defeat was equal to national catastrophe. Terror and occupation divisions destroyed their economic markets and unleashed the rampage of class, ethnic and religious hostilities, which affected generations of people even for decades after the war. Since the summer 1941 though Balkan nations raised to the struggle with fascism. With time partisan fights assumed mass scale and transformed into regular war. It was the main and decisive force there till autumn 1944, when the Red Army approached the Balkans, and constituted an important theatre of the Second World War.