Karpatlar Havzası'na yerleşen ve orada devlet kuran Macarları, beş yüz yıldan daha uzun bir süre boyunca Bizans İmparatorluğu'na bağlayan ilişkilerin tarihinde, İstanbul'un 1204 yılında Haçlılar tarafından işgal edilmesi derinlere işleyen bir değişiklik yaratmıştır. Bunun sonucunda Bizans İmparatorluğu'nun toprakları Laskarislerin, Küçük Asya'daki Nikaia İmparatorluğu denen ülkenin sınırları arasına sıkışmış; bu arada eski başkente ve Propontis'in Avrupa ve Asya'daki kıyı bölgesine Latin imparatorluğunun beyleri el koymuş ve bunların taraftarları Bizans topraklarının doğu ve güney bölgesinde küçük vassal devletler kurmuş; Bizans adalarının ise pek azı dışında tümü Venedik'in egemenliği altına girmiştir. Gerçi Bizanslılar 1261'de İstanbul'u geri aldılar ve imparator VIII. Michael Palaiologos da şimdi artık çok daha dar bir alana sıkışmış olan Bizans İmparatorluğu'nu yeniden kurdu, hatta onu bir süreliğine büyük devlet konumuna da getirdi. Ama haleflerinin hükümdarlığı sırasında gerileme ve çöküş süreci başladı. Bu süreçte iç çekişmeler, politik ve kilisedeki parti savaşlarının keskinleşmesi, durmadan yeniden başlayan iç savaşlar ve Bizans feodalizminin kendine özgü biçimiyle ilişkili bunalım başrolü oynamıştır.

1204 is an important turning point in the relations spanning some five centuries between the Hungarians, who settled and established a new state in the Carpathian basin and the Byzantine empire, when Latins captured Istanbul. The Greeks regained Istanbul in 1261 and the empire was established once again albeit briefly, for soon afterwards it drifted back into decline and decadence. There is an important role in this decline of infighting, of political disagreements, and of the worsening of the conflicts between churches. Ali of these factors had weakened the empire and giyen free rein to neighbouring Serbs, Bulgarians and other western conquerors to carve out chunks of its territory. It alt ended with the Ottomans gaining control over the entire region. Byzantine emperors trapped within the confines of the capital appead for help from the West. They had hopes about Hungary, which was then one of the most powerfull states in Central Europe. A marriage had taken place in 1272 between the Byzantine royal family and the Arpadian dynasty; the house of Palaeologus was the product of this relation. Facing new threats a century later, the Byzantine court sought again the help of Hungary and two emperors travelled to Buda for this purpose. When Turks captured Gallipoli in 1354, attempts were made to unite the Byzantine and the western churches. However these efforts failed and the emperor visited Hungarian King Lajos. The king appealed to Venice and the Pope for organising a crusade but this plan also fell flat chiefly, due to the unresolved conflict between the two churches. The emperor's conversion to the catholic church in 1369 did not help either. In 1389 the Turks entered Hungarian lands for the first time. In the meantime the Byzantine empire had been reduced to a vassal state of the Turks. The emperor asked for western help again, but the crusading army that was assembled for the purpose, was defeated by Turks in Nikeapolis (Niğbolu) in 1396. The Hungarian king Sigismond had to flee. Three years later the Byzantine emperor made a tour of Europe to gam n help, but he was not succesful. In 1402 however, Turks were defeated near Ankara and the empire felt at ease for 20 years. In 1422 the Turks layed siege to Istanbul and the emperor went to Buda and other capitals asking for help. As a result of tong lasting efforts, a union between the churches was agreed in 1439; but this also produced no help when the union was effectively rejected by the people. Help was at last provided at the end of the XV. century by Janos Hunyadi who tried to unite all Balkans against the Turks. He tried in vain to come to rescue when Turks layed siege to Istanbul in 1453 and the city fell to the Turks. Because of his efforts; people honoured and praised Hunyadi in their folk songs and the chronicles; calling him a "Byzantine Emperor".