To understand this more thoroughly let me take you back in time. In the 1460s the political developments in South-East Europe were dominated by the power struggle between the Ottoman Empire, Hungary and Venice.
During the fifteenth century, Ottoman expansion became an increasing threat to Hungary, which the kingdom would not be able to withstand in the long run. Under King John Hunyadi defeats, still alternated with successful military operations, such as the relief of Belgrade in 1456, but neither Matthias I Corvinus nor the Jagiellon kings were able to halt the decline.
When under Süleyman I the Ottomans moved more determinedly against Hungary, the fall of Belgrade in 1521 and the defeat of Mohács in 1526, sealed the fate of the kingdom. At this time the Habsburgs appeared as new opponents, and the Ottoman-Habsburg confrontation began to take shape, which was to characterise political development in South-East Europe in the following centuries.
The Ottoman troops occupied Buda in 1541, sealing the Hungarian kingdom’s division into three parts. The East of the country evolved into the Principality of Transylvania which became a vassal of the Sultan. Western and Northern Hungary came under Habsburg control, while central Hungary was integrated into the Ottoman Empire.
One last successful expansion of Ottoman power was the campaign of 1663/1664 when the fortress Neuhäusel (Nové Zámky in modern Slovakia) on the river Nitra was conquered, the Ottoman Empire has now achieved its greatest geographical extent in South-East Europe.
From the late eighteenth century onwards it was not so much the military power of the Ottoman Empire which determined the extent of Ottoman territories in South-East Europe, but rather the political interests of the other European great powers.
From the nineteenth century onwards, the Ottoman Empire found itself confronted with emerging nationalism within its borders, mostly imported into South-East Europe by elites living in the diaspora. The history of the emergence of the new nation states was part of the “Eastern Question”, the crisis in South-East Europe which grew out of the military decline of the Ottoman Empire and the consequent rivalry among the European powers.
Despite extensive attempts at reforms, Ottoman political leaders were unable to prevent the disintegration of the Empire. When it appeared that the Ottoman army would prevail, Russia entered the war against the Ottoman Empire in 1877. This Russian increase in power met with opposition from the other great powers who attempted a reconciliation of interests during the Congress of Berlin in 1878.
Serbia, Montenegro and Rumania became independent states, and Austria-Hungary obtained the right to administer Bosnia and Herzegovina. The remaining Ottoman territories in South-East Europe (Albania, Macedonia and Thrace) were fought over in the Balkan wars of 1912/1913.
The Balkan Wars were two sharp conflicts that heralded the onset of World War I. In the First Balkan War a loose alliance of Balkan States eliminated the Ottoman Empire from most of Europe. In the Second Balkan War, the erstwhile allies fought among themselves for the Ottoman spoils. All in all, these internecine struggles signified the end of Ottoman rule in South-East Europe, with the exception of parts of Thrace.
In a way, the Balkan wars triggered the First World War (1914-1918), where two opposing alliances assembled. The Allies composing of Austria-Hungary, Germany and from 1914 the Ottomans were fighting against the Central Powers consisted by Russian Empire, France and the United Kingdom.
The first month of combat consisted of bold attacks and rapid troop movements on both fronts. In the west, Germany attacked first Belgium and then France. In the east, Russia attacked both Germany and Austria-Hungary. In the south, Austria-Hungary attacked Serbia. Following the Battle of the Marne (September 5–9, 1914), the western front became entrenched in central France and remained that way for the rest of the war. The fronts in the east also gradually locked into place.
Much of 1915 was dominated by Allied actions against the Ottomans in the Mediterranean. First, Britain and France launched a failed attack on the Dardanelles. This campaign was followed by the British invasion of the Gallipoli Peninsula. Britain also launched a separate campaign against the Turks in Mesopotamia. Although the British had some successes in Mesopotamia, the Gallipoli campaign and the attacks on the Dardanelles resulted in British defeats.
The middle part of the war, 1916 and 1917, was dominated by continued trench warfare in both the east and the west. Though soldiers died by the millions in brutal conditions, neither side had any substantive successor gained any advantage. In early April 1917, the United States, angered by attacks upon its ships in the Atlantic, declared war on Germany. Then, in November, the Bolshevik Revolution prompted Russia to pull out of the war.
Eventually, the governments of both Germany and Austria-Hungary began to lose control as both countries experienced multiple mutinies from within their military structures. The war ended in the late fall of 1918 after the member countries of the Central Powers signed armistice agreements one by one. As a result of these agreements, Austria-Hungary was broken up into several smaller countries.
When compared to its pre-war borders, what was seen as ‘Hungary’ within the Austro-Hungarian Empire, lost nearly 75% of its territory. This land was redistributed to the newly created states of Romania, Czechoslovakia and what was to become Yugoslavia. Nearly 33% of ethnic Hungarians found that they no longer lived in Hungary with nearly 900,000 living in the new Czechoslovakia, 1.6 million in the Transylvania region of Romania and 420,000 in Serbia.