alliances with Sigismund, Holy Roman Emperor, and Jagiellon Poland (taking part in the Battle of Nicopolis), and accepted a peace treaty with the Ottomans in 1417, after Mehmed I took control of Turnu Măgurele and Giurgiu. The two ports remained part of the Ottoman state, with brief interruptions, until 1829. In 1418–1420, Michael I defeated the Ottomans in Severin, only to be killed in battle by the counter-offensive; in 1422, the danger was averted for a short while when Dan II inflicted a defeat on Murad II with the help of Pippo Spano. The peace signed in 1428 inaugurated a period of internal crisis, as Dan had to defend himself against Radu II, who led the first in a series of boyar coalitions against established princes. Victorious in 1431 (the year when the boyar-backed Alexander I Aldea took the throne), boyars were dealt successive blows by Vlad II Dracul (1436–1442; 1443–1447), who nevertheless attempted to compromise between the Ottoman Sultan and the Holy Roman Empire. The following decade was marked by the conflict between the rival houses of Dănești and Drăculești. Faced with both internal and external conflict, Vlad II Dracul reluctantly agreed to pay the tribute demanded of him by the Ottoman Empire, despite his affiliation with the Order of the Dragon, a group of independent noblemen whose creed had been to repel the Ottoman invasion. As part of the tribute, the sons of Vlad II Dracul (Radu cel Frumos and Vlad III Dracula) were taken into Ottoman custody. Recognizing the Christian resistance to their invasion, leaders of the Ottoman Empire released Vlad III to rule in 1448 after his father's assassination in 1447. Known as Vlad III the Impaler or Vlad III Dracula, he immediately put to death the boyars who had conspired against his father, and was characterized as both a national hero and a cruel tyrant. He was cheered for restoring order to a destabilized principality, yet showed no mercy toward thieves, murderers or anyone who plotted against his rule. Vlad demonstrated his intolerance for criminals by utilizing impalement as a form of execution. Vlad fiercely resisted Ottoman rule, having both repelled the Ottomans and been pushed back several times. The Transylvanian Saxons were also furious with him for strengthening the borders of Wallachia, which interfered with their control of trade routes. In retaliation, the Saxons distributed grotesque poems of cruelty and other propaganda, demonizing Vlad