Murad II (1421–1451) rebuilt Ottoman power after the Interregnum, twice abdicated for the contemplative life, and twice returned — to destroy the Varna crusade (1444) and Hunyadi at the second Kosovo (1448).
Murad II spent his first decade burying the Interregnum's ghosts — a pretender uncle strangled at Edirne after a Byzantine-sponsored civil war, the 1422 siege of Constantinople as the receipt — and his middle years fighting the long Hungarian-Venetian coalition on the Danube and the sea.
In 1444, peace signed and son enthroned, he retired to Manisa — and the Christian powers tore up the treaty. Recalled, he destroyed the crusade at Varna in November 1444, put down the Janissaries' price for his second return, and finished the argument with Hunyadi at Kosovo in 1448. The son he twice stepped aside for was Mehmed the Conqueror.
Born at Amasya in 1404, in the middle of the fratricidal Interregnum, Murad was governor of the same province as a boy while his father Mehmed I stitched the empire back together. He succeeded at seventeen in 1421 — and Byzantium promptly released the pretender "False" Mustafa against him, the last play of the old policy of feeding Ottoman civil wars.
Murad crushed it within a year, hanged his uncle from Edirne's walls, blinded the brothers a looser age might have spared, and laid siege to Constantinople in 1422 as punishment — lifting it only when a genuine brother's revolt, also Byzantine-encouraged, called him to Anatolia.
Murad is the sultan contemporaries found easiest to like and hardest to explain. The Greek historians — Doukas, Chalkokondyles — dwell on his fidelity to treaties, his mercy in victory, his distaste for conquest beyond necessity: judgments almost unheard-of from Byzantine pens about Ottoman rulers. The dervish orders and poets he patronised at Edirne remembered the mystic's temperament under the armour; his will, asking burial in the open ground at Bursa so the rain of God might fall on him, was its own character sketch.
The double abdication proves the inclination was real — no medieval monarch played at renunciation twice — and the double return proves the discipline that overrode it. At Varna, with the battle wavering and the broken treaty nailed to a lance as the army's standard, the retired mystic commanded the centre that held; the combination of contemplative longing and battlefield iron is the man entire.
The pattern of the middle years was coalition management: Venice fought over Thessalonica (stormed 1430), Hungary over the Danube line, Karaman gnawing from Anatolia whenever the West attacked — and Hunyadi's "Long Campaign" of 1443 breaking deep into the Balkans until winter and the Zlatica passes stopped it. The peace of Szeged in summer 1444 gave back Serbia to Branković and swore ten years' truce; Murad, mourning his eldest son, enthroned the twelve-year-old Mehmed and withdrew to Manisa.
Within weeks the cardinal-legate absolved Hungary of the oath, and the crusade marched for Varna to meet the Venetian fleet. Murad, ferried across the Bosphorus under Genoese sail past the useless blockade, took command: on 10 November 1444 King Władysław III died charging the Janissary line, Cardinal Cesarini died in the rout, and the last crusade for Constantinople died with them. The Janissary mutiny that forced Murad's formal second reign (1446) and the three-day slaughter of the second Kosovo (October 1448) — Hunyadi's last great army broken — completed the settlement his son would inherit: a Balkans without a rescuer.
Murad handed Mehmed II an instrument no Ottoman ruler had yet possessed: frontiers quiet by exhaustion of every enemy, the Janissary machine tempered at Varna and Kosovo, and a treasury and administration the Halil Çandarlı vizierate had kept in careful order. The conquest of 1453 was planned within two years of his grave — with his army.
His Edirne — the poets' and dervishes' court, the great mosque complexes — marks the moment Ottoman high culture found its classical voice; and his tomb at Bursa, earth open to the sky as he asked, remains the dynasty's most eloquent monument precisely for its refusal of monument.