Conquests by who began the transformation of the Ottoman sultanate into an Empire?
The Ottoman Empire (/ˈɒtəmən/; Ottoman Turkish: دَوْلَتِ عَلِيّهٔ عُثمَانِیّه‎ Devlet-i Aliyye-i Osmâniyye, Modern Turkish: Osmanlı İmparatorluğu or Osmanlı Devleti), also known as the Turkish Empire, Ottoman Turkey or Turkey, was an empire founded in 1299 by Oghuz Turks under Osman I in northwestern Anatolia. After conquests in the Balkans by Murad I between 1362 and 1389, the Ottoman sultanate was transformed into a transcontinental empire and claimant to the caliphate. The Ottomans ended the Byzantine Empire with the 1453 conquest of Constantinople by Mehmed the Conqueror.