Hungarian irredentism or Greater Hungary is a broad umbrella term consisting of irredentist and revisionist political ideas. The idea is associated with Hungarian revisionism. Its goal is to restore the pre-World War I borders of the Kingdom of Hungary, or at least to regain control over Hungarian populated areas in Hungary's neighbouring countries.
The Treaty of Trianon defined the borders of the new independent Hungary and, compared against the claims of the pre-war Kingdom, new Hungary had approximately 72% less land stake and about two-thirds less inhabitants, almost 5 million of these being of Hungarian ethnicity. However, only the 54% of the inhabitants of the pre-war Kingdom of Hungary were Hungarians before the World War I. Following the treaty's instatement, Hungarian leaders became inclined towards revoking some of its terms. This political aim gained greater attention and was a serious national concern up through the second World War.
Hungary, supported by the Axis Powers, was successful temporarily in gaining some (primarily ethnic Hungarian) regions of the former Kingdom in the First and Second Vienna Awards of 1938 and 1940, and through military campaign gained regions of Carpathian Ruthenia in 1939 and (ethnically mixed) Bačka, Baranja, Međimurje, and Prekmurje in 1941 (Hungarian occupation of Yugoslav territories). Following the close of World War II, the borders of Hungary as defined by the Treaty of Trianon were restored, except for three Hungarian villages that were transferred to Czechoslovakia. These villages are today administratively a part of Bratislava.
The independent Kingdom of Hungary was established in 1000 AD, and remained a regional power in Central Europe until Ottoman Empire conquered its central part in 1526 following the Battle of Mohács. In 1541 the territory of the former Kingdom of Hungary was divided into three portions: in the west and north, Habsburg Kingdom of Hungary retained its existence under Habsburg rule; the Ottomans controlled the south-central parts of former Kingdom of Hungary; while in the east, the Eastern Hungarian Kingdom (later the Principality of Transylvania) was formed as a semi-independent entity under Ottoman suzerainty. After the Ottoman conquest in the Kingdom of Hungary, the ethnic structure of the kingdom started to become more multi-ethnic because of immigration to the sparsely populated areas. Between 1683 and 1717, the Habsburg Monarchy conquered all the Ottoman territories that were part of the Kingdom of Hungary before 1526, and incorporated some of these areas into the Habsburg Kingdom of Hungary.