The alliance of the seven Hungarian tribes took possession of the then largely uninhabited Carpathian Basin. Until then, the sparse Slavic population of the north-western Carpathians had lived under Moravian rule for a few decades after the collapse of the Avar Khaganate in the early 9th century.

The Kingdom of Hungary was established with the coronation of King Stephen I. He converted the Hungarians to Christianity and created two archdioceses (Esztergom and Kalocsa) and ten dioceses. He divided Hungary into counties led by ispáns, who were appointed by the king.

The hordes of the Mongol Empire invaded Hungary and almost completely destroyed it. One third to one half of the population was destroyed. The Mongols also suffered heavy losses in the battle of Muhi and they could not hunt down the king. After their withdrawal, King Béla IV reorganized Hungary. He allowed the feudal lords to build stone castles because they were able to successfully resist the nomadic Mongols. The vast majority of stone castles were built after this. The king called in German, Vlach (Romanian) and Slavic settlers to replace the destroyed population.

Sultan Suleiman I launched a war against Vienna, instigated by the French. Ferdinand I, Duke of Austria, was the brother-in-law of King Louis II of Hungary. The army of the Ottoman Empire defeated the much smaller Hungarian army at Mohács, and King Louis II died in the battle. A group of the barons elected Ferdinand I of the House of Habsburg to the throne, who promised to defend Hungary from the Turks. He was the younger brother of the most powerful European monarch Emperor Charles V. But the nobility chose the most powerful Hungarian baron, Szapolyai János, who was also crowned as King John I. The country was split in two and a decades-long struggle for power began.

The Turks conquered Buda, the capital of Hungary, after the death of King John I. The central part of the country was under Turkish rule for 150 years. The western and northern parts (including present-day Slovakia) formed the Kingdom of Hungary ruled by the Habsburg emperors. The eastern parts (now mainly under Romanian rule) were ruled by the successors of King John I of Hungary, who later established the Principality of Transylvania.

John II (John Sigismund), the son of King John I of Hungary, renounced the title of King of Hungary in favor of King Maximilian of the House of Habsburg, and henceforth held the title of Prince. This formally created the Principality of Transylvania, which was the eastern half of Hungary not ruled by the Habsburgs and was also a vassal of the Ottoman Empire. John II died in 1571, after which the three nations of Transylvania (the Hungarian nobility, the Székelys and the Saxons) elected the prince.