The defeat at Ankara opened a period of political instability combined with social strife. Until 1413 there were sometimes two, sometimes three Ottoman states in conflict with one another. This period is known as the interregnum (fetret devri). Dynastic clashes and social upheaval were to continue within the Ottoman Empire until 1425.
After the conclusion of the treaty and the evacuation of Anatolia by the Mongol army, Suleyman, aiming at sole supremacy over the Ottomans, focused his attention on his two rival brothers. With this end in view, he crossed into Anatolia. It is not clear whom he entrusted with the administration of Rumelia since his vizier, Ali Djandarh, accompanied him. In all likelihood Rumelia was left in the hands of the udj beys. The territory, whose economy had originally been geared to war and conquest, was now confronted with serious problems resulting from the peace, the more so as the number of warriors assembled there had increased with the arrival of those fleeing before the Mongols. However, peaceful relations on the whole were maintained with the neighbouring Christian states, including Hungary which, since the 1360s, had constituted the only real menace to the Ottomans in the Balkans. Furthermore, the Hungarians began to control the production and distribution of metals in central Europe. In Bayazid I’s days King Sigismund of Hungary caused trouble by exerting influence upon several Balkan states. His purpose was to expand his realm from the Black Sea to the Adriatic coast. Nevertheless, his projects regarding the Dalmatian ports caused anxiety to Venice, which avoided an alliance with him against the Turks. Furthermore, during the years following the battle of Ankara, Sigismund was entangled in dynastic strife against his rival, Ladislas of Naples. On the other hand, Ottoman relations with the Venetians, who had occupied some ports in Albania and in Greece, provoked limited military action, the Turks retaliating by harassing Venetian territories and inflicting damage upon Venetian merchants. A new treaty negotiated by Suleyman ended the dispute, the Venetians agreeing to pay annual tribute to him for their new possessions.
In Anatolia Suleyman was first able to eliminate his brother Isa. Early in 1404 he occupied the old capital, Bursa, and the important town of Ankara. He then annexed the Black Sea coast between Herakleia and Samsun, as well as the region of Smyrna, where he obliged Djuneyd to recognise his overlordship. After Timur’s death (1405) the Mongol grasp over Anatolia weakened, and Suleyman was free to turn against his other brother, Mehemmed. The latter, established in a predominantly Turkish milieu, extended his rule from Amasya up to Sivas and consolidated his position by maintaining good relations with the Karamanoglu and with the neighbouring nomadic populations. By marrying the daughter of Dhulkadir, the emir of Elbistan, he obtained access to important military manpower deriving from the tribes of that region. He alone proceeded to assume the title of sultan. A few clashes between the two Ottoman princes came to nothing, and Mehemmed decided to transfer operations to Rumelia.
The instrument of his plans was a fourth brother, Musa, whom he despatched to Rumelia in 1409 with the help of the Isfendiyaroglu. The Byzantine emperor, the Venetians, the Serb ruler and, above all, the Wallachian voivode, Mircea, watching Suleyman’s strong position with anxiety, were ready to support Musa. Mircea received him in his territories and helped him to make preparations against Suleyman. When the latter was obliged to return to Rumelia in 1410, Mehemmed easily became the lord of the whole of Ottoman Anatolia. After a series of military operations, Musa emerged victorious, while Suleyman lost his life in February 1411.
At the beginning Musa, established in Edirne, governed the European provinces as a vassal of his brother, Mehemmed, who had moved to Bursa. When still fighting against Suleyman, Musa repudiated promises made to the Christian lords who had supported him, and revived the spirit of the holy war. Thus he won the support of the military who had long refrained from raiding Christian territories. He soon launched attacks on all directions and besieged Thessalonica and Constantinople.
Alarmed, the Christian lords turned to Mehemmed. Several high Ottoman officials, who had been connected with Suleyman’s administration and, for this reason, had been persecuted by Musa, also joined Mehemmed, and a new struggle for sole supremacy over the Ottoman state began in 1412. For a while, Musa’s position appeared strong, but defections to Mehemmed’s side increased while the Byzantine emperor also offered him his help. Musa was finally defeated near Sofia and killed in 1413. The period of the interregnum was now ended, Mehemmed becoming the sultan of a reunited state and being generally recognised as his father’s legitimate successor. Official Ottoman tradition would never consider Suleyman and Musa as real sultans.
Mehemmed, well aware that his territories had been devastated by the civil wars and that the unity of his state was only fragile, adopted a policy of peace towards the Christians. His intention was facilitated by the hostility prevailing among his main enemies, Venice and Hungary. Having insured peace in Rumelia, the sultan consolidated his position in Anatolia by defeating the Karamanoglu, who, profiting from the civil war, had besieged Bursa. He also put a temporary end to the separatist movement of Djuneyd in Smyrna, whom he sent to Nicopolis as an udj bey of the Danube frontier.
The Christian enemies of the Ottoman state tried to divide it once again, and a new pretender to the Ottoman throne appeared on the scene with the help of the Byzantines, the Wallachians and the Venetians, who now had established contacts with the emir of Karaman. He was Mustafa, who passed into history as the ‘false’ one (duyme) because Mehemmed’s milieu claimed that he was not Bayazid I’s son at all, but simply an impostor. Like Musa, Mustafa, with the help of the voivode Mircea, set off from Wallachia. Djuneyd joined him, abandoning his post at Nikopolis. Soon both were defeated by Mehemmed’s troops near Thessalonica and compelled to take refuge with the Byzantines (1416).
It was now becoming apparent that the internal strife which had shaken the Ottoman state for more than a decade was not only a dynastic strife but was also connected with deep social problems. A revolution broke out under the spiritual leadership of the theologian and mystic, Sheyh Bedr ed-din, who had been Musa’s judge of the army (kazjaskef)? The popular masses, especially in the region of Aydin, participated wholeheartedly in the movement which was also supported by some Greek Orthodox monks. The rebels preached common ownership of fields and cattle, farm implements, food and clothing; also fraternisation with the Christians because, according to them, communion with the Christian faith was the only way to ensure the salvation of the soul. This last point suggests that the aim of the revolt was possibly a state based on a new religion deriving from both Islam and Christianity.
These doctrines certainly originated from the continuous political change and the religious confusion which went on for a long period in the Turkish territories. The political change, at first due to the existence of several Turkish states and the resulting strife among them, was exacerbated by Timur’s occupation of Anatolia, while the disruptive civil wars made the lower classes poorer and therefore more ready to demand social change. The problem of the religious confusion was more complicated. Islam was certainly the religion of the conquerors, and the ruling group preached the principle of holy war, on which expansion was based. Nevertheless, this religion remained unorthodox in Anatolia. Beside the administrative authorities who were usually traditional Muslims and often theologians (ulema), there existed the nomads who had been recently and superficially Islamised so that they preserved their pagan or shamanistic beliefs. A few of the nomadic tribes were Christian causing additional confusion. Dervishes often visited the newly conquered territories to preach Islam, but they largely belonged to sectarian and mystical circles, preferring to move away from central Islamic lands in order to diffuse their kind of faith with greater freedom. On the other hand, the subjugated Christian population of Anatolia had a long religious and cultural tradition, and for this reason was able to exercise considerable and varied influence upon the new masters. In the newly conquered Balkans, the Turks were in the minority. Mixed marriages were usual as large numbers of warriors from all over the Islamic world were attracted to the Turkish territories, situated between the Christian and the Muslim lands, to carry out holy war. These warriors had to find their women among their enemies, often among the prisoners. Sheyh Bedr ed-din himself was the son of a Muslim judge, established in Rumelia since the very early years of the conquest, and of the daughter of the Byzantine governor of a provincial town, who had been taken prisoner. Mixed marriages certainly meant a certain religious confusion among families which was to affect the whole of society. The situation was underlined at the end of the fourteenth century by a Muslim preacher in Bursa who said that Jesus was not inferior to the prophet Muhammad; also by the great mystical poet, Yunus Emre, who wrote that his soul at one moment prayed in a mosque and at another moment read the gospel in a church.
Bedr ed-din’s movement shook the foundations of the Ottoman state as it propagated fraternisation with the Christians, an ideal quite contrary to that of the holy war. It also threatened the Greek Orthodox Church which, enjoying the protection of the sultans, had its place insured under Ottoman domination. The revolution was therefore suppressed through military operations followed by a bloody massacre of men, women and children organised by Mehemmed I. Bedr ed-din himself was hanged in Serres. Nevertheless, an order of dervishes, the Torlak, professing that Jesus was God, survived.
Mehemmed I had overcome the deep crisis, but his position became even weaker as the Venetians profited from the situation by destroying the Ottoman fleet at Kallipolis (May 1416). The sultan now revised his former policy of peace towards the Christians. In 1417 he launched a large-scale punitive campaign against Wallachian territories and reduced the voivode, Mircea, to the status of a tribute-paying vassal. Another Ottoman army marched to Albania and conquered the strategically important port of Avlona at the entrance to the Adriatic, and, in the following year, the strong fortress of Argyrokastron. Mehemmed then undertook a new expedition against the Danubian territories which was also crowned by diplomatic success when he managed to isolate King Sigismund of Hungary from two of his allies, W-adyslaw of Poland and Vytautas (Vitold), the grand duke of Lithuania (1420).
Mehemmed I died in May 1421 and he was succeeded by his son, Murad II. Dynastic strife, however, resumed. The Byzantines, aiming once again at the division of the Ottomans, set against Murad the pretender Duzme Mustafa and Djuneyd, both of whom had been in their hands since 1416. Their effort failed as Adorno, the Genoese podesta of Phocaea, put his fleet at the disposal of Murad II, who crossed to Thrace and eliminated Mustafa. The sultan also retaliated against the Byzantines by attacking their territories and especially by besieging Constantinople in the summer of 1422. The Byzantines then attempted to compel him to abandon the siege by supporting another pretender, his young brother, Mustafa, acclaimed sultan in Nicaea. However, Murad defeated him and put him to death.
The civil wars gave the opportunity to the Turkish emirs to move against the Ottomans. The Isfendiyaroglu invaded the territories of Sangarios, while the Karamanoglu tried to seize the important harbour of Antalya. The sultan was able to overcome these troubles, too. Djuneyd once again strove to establish his own state in Smyrna in collaboration with a new pretender, Duzme Mustafa’s young son. In 1424 the sultan concluded a treaty with the Byzantines and another one with the Hungarians. Peace in the Balkans enabled him to overcome this pretender, too, and he despatched troops to Aydin who exterminated Djuneyd and his whole family. The region of Aydin, as well as the neighbouring emirate of Menteshe, was then annexed to the Ottoman lands. About that time the region of Samsun, on the Black Sea, was also annexed. Murad II, having emerged victorious from these dynastic wars, probably wanted to have the restoration of his rule over Asia Minor publicly recognised, and he invited representatives of the Byzantine emperor, the Wallachian voivode, the Serb ruler and other Christian lords to Ephesus that year (1425).