=== Conflicts with the
Aydinids === During the civil war in Byzantium both
Palaiologos and
Kantakouzenos were trying to find external allies and used foreign mercenaries. The Bulgarian Emperor supported the first opponent whose stronghold was Constantinople. John Kantakouzenos on the other hand regularly hired Ottoman Turk mercenaries from
Asia Minor who soon became a fixture on the battlefields in
Thrace. The Byzantines often lost control over the Ottomans then as the latter regularly plundered villages in the Southern Balkans after the 1320s. ,896. In 1344,
Momchil, the independent Bulgarian ruler of the
Rhodope and
Aegean regions, whose army grew to 2,000 men, took an important role in the Byzantine civil war. While at first he supported John Kantakouzenos, from the spring of 1344 Momchil reneged, provoked by the aggression of the Ottoman allies. In June, he defeated the Aydinid fleet near Portogalos Bay. According to sources, at night the Bulgarian ruler sent boats to burn the anchored Aydinid ships and soon after he defeated the army of Kantakouzenos at
Mosynopolis. Soon after, on 7 July 1345, Aydinid forces under Umur Beg defeated Momchil's army in the
Battle of Peritor near his capital
Xanthi. Sources attest that the independent ruler perished in the battle without leaving a successor, and with little political will or leadership left to counter the Ottoman invasion.
First clashes with the Ottomans During the Byzantine civil wars Ivan Alexander regained control over several towns in Thrace and the Rhodopes but his frequent interference in the internal affairs of Byzantium hampered any closer relations between the two countries despite the peace established in 1332. In 1352 Turkish forces invaded Bulgaria anew, raiding Thrace, particularly the vicinities of
Aitos,
Yambol, and
Plovdiv, and capturing rich spoils. In the same year the Ottomans seized their first fortress on the Balkans, Tsimpe on the
Gallipoli peninsula, setting firm foot in Europe. Until 1354 Ottoman forces again ravaged the lands around Yambol and Plovdiv as well as the lower valleys of the
Maritsa and
Tundzha rivers. In 1355 the Ottomans launched a campaign towards
Sofia, but were soon engaged by the army of Ivan Alexander's eldest son and heir
Michael Asen close to
Ihtiman. In the
following battle both sides suffered heavy casualties and, despite the death of young Michael Asen, the Turks were unable to reach Sofia.
Unsuccessful alliance The defeat raised serious alert not only in Tarnovo, but also in Constantinople, forcing John Kantakouzenos to abdicate and removing one of the main facilitators of the Ottoman invasion. Faced with threat, Bulgaria and Byzantium made an attempt for rapprochement. In 1355 a daughter of the Bulgarian Emperor,
Keratsa, married
Andronikos, the infant son of the new Byzantine Emperor
John V Palaiologos. Unfortunately, the new relations between the houses of Tarnovo and Constantinople did not live up to the expectations of mounting a more significant response to the invading Ottomans. After the death of
Stefan Dušan on 20 December 1355, the
Serbian Empire lost much of its hegemony in the Western Balkans and the large and ethnically diverse empire split into several successor states. The Bulgarian and Byzantine Empires of the period were once again the only remaining major political powers on the peninsula with the potential to stop the Ottoman expansion. Between 1354 and 1364 the Turks conquered
Thrace as a number of important fortresses and towns, such as Plovdiv and
Stara Zagora fell under attack. From the end of the 1350s Ottoman military units even reached the surroundings of the capital as, according to sources, the Emperor took precautions to strengthen the city walls. Ottoman chronicler
Hoca Sadeddin Efendi suggests that Turkish advance between 1359 and 1364 involved destruction and depopulation of many areas: the towns
Plovdiv,
Stara Zagora, and
Sliven were devastated, and others such as Venets and Sotirgrad were completely destroyed. Destruction was accompanied by slaughter and deportation of the local populace to Asia Minor. Not only was there a total lack of coordination between the two Empires, but they also quarreled over the
Black Sea ports of
Mesembria and
Anchialos. Bulgaria successfully defended them in 1364, but the continuing conflict deepened the distrust and animosity between the two states despite the impending danger.
Last years of Ivan Alexander Apart from the economic devastation and military threat from the south, Bulgaria had other problems: in 1365 the
Hungarian King Louis I invaded northwestern Bulgaria, seizing the important Vidin fortress and capturing the eldest living son of the tsar,
Ivan Sratsimir. In his unsuccessful initial attempts to retake Vidin, Ivan Alexander even resorted to using Ottoman mercenaries. Eventually, in the summer of 1369, the Bulgarian Emperor restored his authority over the Vidin Province with the help of the
Wallachian
voivode Vladislav I, but that proved to be his last success. After Ivan Alexander's death on 17 February 1371, the lands populated by Bulgarians were divided into several independent states. Much of the former territory of the
Second Bulgarian Empire came under the rule of the tsar's third son
Ivan Shishman; the
northwestern areas were the dominance of the eldest son
Ivan Sratsimir,
despot Dobrotitsa held
Dobruja, and most of
Macedonia was divided into several feudal states controlled by Serbian nobles. == Battle of Chernomen and its consequences ==