From 1430 onwards the Ottomans, under Sultan Murad II, began a campaign to recover their lost Balkan territories. By 1439 they had taken Borač, Zvornik and Srebrenica, and by 1440 Serbia had become an Ottoman province. In 1444 Murad heavily defeated a crusading army of Poles, Hungarians, Croatians, Serbs and Wallachians at the battle of Varna, and in 1448 he achieved a further important victory over a Hungarian force in the second battle of Kosovo. These gains left the Ottomans free to contemplate an attack on the Byzantine capital itself, Constantinople. In April 1453 Murad’s son Mehmed II laid siege to the city, which by that time was in a weak, dilapidated state, under the shaky command of Emperor Constantine XI Palaiologos. Thanks to the Turks’ novel use of gunpowder, the siege lasted just 53 days, and when it ended Mehmed moved the Ottoman capital there from Adrianople. The Ottomans were now in control a large area of the Balkans and in a position to advance further northwards and westwards. Their annexations of Morea (the Greek Peloponnese) and Bulgaria were soon to follow. The fall of Constantinople marked the end of the once mighty, 1,500-year-old Byzantine (East Roman) Empire and is widely considered a pivotal moment in European history.
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