The newly independent Bulgarian state, ruled by the new Asenid dynasty from its capital at Veliko Türnovo, comes to be known as the “empire of Vlachs and Bulgars,” or the Second Bulgarian Empire.

After the major Bulgarian success in the battle of Tryavna in 1190, their troops have launched frequent attacks on Thrace and Macedonia to liberate all Bulgarian lands.

The imperial troops cannot confront the fast Bulgarian cavalry, which attacks from different directions on a vast area.

Towards 1194, Ivan Asen takes the important city of Sofia and the surrounding areas as well as the upper valley of the Struma River, whence his armies advance deep into Macedonia.

To distract his attention the imperial forces decides to strike in an eastern direction.

They assembled the Eastern army under its commander Alexios Gidos and the Western army under its Domestic Basil Vatatzes to stop the rise of Bulgarian power.

Basil Vatatzes, a Greek nobleman and general, is married to a niece of Emperor Isaac II Angelos and had been appointed by him as Domestic of the East and doux of the Thracesians.

In this capacity, he had suppressed the revolt of Theodore Mankaphas in Philadelphia in 1189.

By 1193, he was Domestic of the West (as with his contemporary and co-commander, Alexios Gidos, it is unclear if he was Grand Domestic or not), at Adrianople.

He is probably the father of John III Doukas Vatatzes, the future Emperor of Nicaea, and of the sebastokrator Isaac Doukas Vatatzes.

Near Arcadiopolis in Eastern Thrace, the imperial armies meet the Bulgarian army and, after a fierce battle, are annihilated.

Most of Gidos's troops perish and he has to flee for his life, escaping only with great difficulty, while the Western army is slaughtered completely and Basil Vatatzes is killed on the battlefield.

Theodore Laskaris, Empire of Nicaea, the center of the Orthodox church and imperial government in exile, had in 1214 concluded a peace treaty with the Latin Empire at Nymphaion, and in 1219 he had married a niece of Emperor Henry.

In spite of predominantly peaceful relations, Theodore had attacked the Latin Empire again in 1220, but peace was restored after he negotiates a settlement with Robert of Courtenay, fourth emperor of the Latin Empire of Constantinople, to whom he betroths his daughter Eudocia.

By his courage and military skill, he has enabled the imperial Greek state not merely to survive, but ultimately to beat back the Latin invasion.

The ruler of a territory roughly coterminous with the old Roman provinces of Asia and Bithynia, Theodore dies in November 1221.

John Doukas Vatatzes, a successful soldier from a military family, is probably the son of the general Basileios Vatatzes, Duke of Thrace, who died in 1193, and his wife, an unnamed daughter of Isaakios Angelos and cousin of the Emperors Isaac II Angelos and Alexios III Angelos.

The Vatatzes family had first become socially prominent in the Komnenian period and had forged early imperial connections when Theodore Vatatzes married the porphyrogenete princess Eudokia Komnene, daughter of Emperor John II Komnenos.

John had been chosen by Theodore as husband for his daughter Irene and as heir to the throne, excluding members of the Laskarid family from the succession.

He ascends the throne of Nicaea as Emperor John III in mid-December 1221.

Theodore's surviving brothers, Alexios and Isaac, protest the succession, and civil war breaks out.

The struggle for the Nicaean throne ends with the Battle of Poimanenon, fought in the winter of 1223/1224, in which John’s opponents, the two Lascaris brothers, are defeated and blinded in spite of the support they had acquired from the Latin Empire of Constantinople.

This victory opens the way for the recovery of most of the Latin possessions in Asia.

The crusaders of the Latin Empire of Constantinople had been decisively defeated by the Bulgarian Emperor Kaloyan in the battle of Adrianople (1205).

In 1225, Theodore Komnenos Doukas, self-proclaimed despot of Epirus, proclaims himself emperor in a direct challenge to the identical claim of Nicaean emperor John III.

Nicaean forces dispatched by John to fight Epirus lose at Adrianople in Thrace, and Theodore takes possession of the city.

John III, allied in 1224 to Bulgarian ruler Ivan II, had acquired territory in the Aegean and in Asia Minor but had failed to capture Constantinople.

Ivan had subsequently defected to the Latin side, but the Latin emperor Robert, threatened both by Nicaea in Asia and Epirus in Europe, sues for peace, which is concluded in 1225.

According to its terms, the Latins abandon all their Asian possessions except for the eastern shore of the Bosporus and the city of Nicomedia with the surrounding region.

Seljuq sultan 'Ala' ad-Din Kayqubad has meanwhile built on the accomplishments of his father and brother, having conquered most of the Mediterranean littoral up to the frontiers of Syria from 1221 to 1225.

John III Doukas Vatatzes of Nicaea had no sooner taken Adrianople in 1225 than  Theodore had arrived and taken it from him in turn.

Theodore had also allied with the Bulgarians and had driven the Latins from Thrace.

Elated by his success, Theodore arranges for his coronation as emperor in 1225 or 1227 by the autocephalous archbishop of Ohrid, Demetrios Chomatianos, although this is not recognized by most Greeks, especially not the Patriarch in Nicaea.

John III, emperor at Nicaea and regent for young Baldwin II, his grandson, seeks to retake Constantinople from the Latins before his rivals Theodore Angelus Doukas, despot of Epirus, or Ivan Asen II, Tsar of Bulgaria.

The despots of Epirus and Thessaly, who had saved much of northern Greece from Western conquest after 1204, are direct descendants of Constantine Angelos and Theodora, daughter of Emperor Alexios I Komnenos.

Theodore Komnenos Doukas, who had earlier seized Thessalonica and been crowned emperor there, marches on Constantinople, but his rivals, the Nicaean emperor and the Bulgarian tsar, attack him from the east and north.