Following the fall of Constantinople, he served Theodore I Laskaris, founder of the Empire of Nicaea, for a few years before being called to Epirus, where his half-brother Michael I Komnenos Doukas had founded an independent principality.

Bardanes writes that Theodore "took many dangers for his sake and wrested many fortresses from the enemies and subdued them to Laskaris' rule", distinguishing himself through his valour and receiving many rewards from the Nicaean ruler.

[13] From 1210 on, Michael I Komnenos Doukas was engaged in territorial expansion, chiefly at the expense of the Latin Kingdom of Thessalonica to his east; after initial reverses, much of Thessaly was conquered.

The Archbishop of Ohrid, Demetrios Chomatianos, refused to sanction the marriage due to consanguinity—Theodora was a second cousin of Stefan Radoslav's mother, Eudokia Angelina, a daughter of Alexios III Angelos.

[24] With his position thus strengthened, Theodore expanded his territory into northern Macedonia, although it is possible that at least part of this region had already been captured by Michael I after the death of the local Bulgarian ruler Strez in 1214.

It is unclear to what extent Theodore's expansion involved direct conflict with the Bulgarian Tsar Boril (r. 1207–1218), but by 1217 he held Ohrid, Prilep, and most of the plain of Pelagonia, at least up to Strez's old capital at Prosek, and likely beyond, approaching the Strymon River.

[25] As the Greek historian Konstantinos Varzos has noted, the capture of Ohrid, seat of the eponymous archbishopric, was particularly important for the standing of the Epirote state and Theodore's aspirations.

[27] Already under Michael I, two local synods of bishops had emerged in the Epirote domains to carry on administration of the Church, largely independent of the Patriarch, one at Naupaktos under John Apokaukos, and one at Ohrid under Chomatianos.

[28] Despite his close ties to Epirus, Stefan II Nemanjić exploited the Epirote–Nicaean rivalry to his advantage to secure autocephaly for the Serbian Church, which traditionally had been under the jurisdiction of the Archbishop of Ohrid.

Brushing aside Chomatianos' vehement objections, Stefan managed to have his brother Rastko, renamed Sava, consecrated by Manuel Sarantenos as autocephalous archbishop of Serbia in 1219.

The death of the warlike Henry, followed by that of Pope Innocent III, the instigator of the Fourth Crusade, a month later, was a major stroke of good fortune for Theodore as it removed two of his most eminent and capable opponents.

As in the Norman invasion of William II of Sicily (r. 1166–1189) in 1185, Peter intended (after capturing Dyrrhachium) to follow the ancient Via Egnatia to Thessalonica, wresting Albania and Macedonia from Epirote control in the process.

[37][38] The commonly accepted version of events is that Dyrrhachium resisted with success, and as his casualties mounted Peter was forced to raise the siege and start his march towards Thessalonica.

[41] Akropolites, the chronicler Ephraim, and some Western sources on the other hand claim that Dyrrhachium was captured, and are followed by some modern scholars, including the Greek I. D. Romanos and the French Alain Ducellier.

As the historian John Van Antwerp Fine remarks, "it is not important which version is correct"; the outcome was the same, and if lost, Dyrrhachium was quickly retaken after Peter's capture.

A politically astute ruler, Yolanda also secured her eastern border by offering her daughter Maria of Courtenay in marriage to Theodore Laskaris, who had just been widowed for the second time.

[47] Before launching his final stroke against Thessalonica, Theodore also took care to secure his southern flank, by appointing his brother Constantine Komnenos Doukas as governor in Aetolia and Acarnania.

[32][49] As the fall of Thessalonica appeared imminent, Pope Honorius excommunicated Theodore, ordered an embargo on horses, troops, and supplies from the Adriatic ports, and sent letters to Constantinople urging assistance to Demetrius.

[50] In the meantime, the Latin Empire, now under Robert of Courtenay (r. 1221–1228), was once more embroiled in warfare with Nicaea as it supported Laskaris' brothers in their challenge against the new Nicaean emperor, John III Doukas Vatatzes (r. 1222–1254).

[31] The first detachments of the assembling crusade, under Count Oberto II of Biandrate, arrived at Thessalonica in summer 1222 and joined the de facto regent, Guy Pallavicini.

Theodore's brothers Manuel and Constantine were raised to the rank of Despot, the long-serving John Plytos became panhypersebastos and mesazon (chief minister), and a number of scions of old Byzantine aristocratic families, who had sought refuge in Epirus, were appointed as provincial governors alongside members of the local aristocracy.

[74][75] Already in 1224, or at least in 1225, Theodore captured Chalcidice with Mount Athos,[74] and in spring 1225, he advanced through eastern Macedonia and western Thrace, seizing Christopolis, Xanthi, Gratianopolis, Mosynopolis and Didymoteicho.

His domain was reduced to the environs of the city and his family's core territories in Epirus and Thessaly, as well as Dyrrhachium and Corfu, while his brother Constantine in Aetolia and Acarnania recognized his suzerainty.

[100][103] He received widespread support in the province, perhaps even from the local governor, Michael I's son-in-law Constantine Maliasenos, allowing him to raise an army and in a short time occupy Farsala, Larissa, and Platamon.

Manuel renounced his allegiance to Vatatzes and received Thessaly, John and Theodore kept Thessalonica and the remaining parts of Macedonia as far west as Vodena and Ostrovo, and Constantine was confirmed in his appanage of Aetolia and Acarnania.

Coupled with the increasingly deteriorating situation of the Latin Empire, this development left John Vatatzes of Nicaea as the pre-eminent ruler of the region, and the obvious candidate for the capture of Constantinople.

On John's death he raised his younger son Demetrios Angelos Doukas (r. 1244–1246) in his place, and sent an embassy to Nicaea to announce the succession, as befitted the terms of vassalage agreed in 1242.

[113][114] At the close of this campaign in November, as Vatatzes was encamped at Melnik, he was informed of a conspiracy to depose Demetrios and deliver Thessalonica to him in exchange for a chrysobull guaranteeing the traditional rights and privileges of the city.

[118][119] The modern biographer of the Komnenoi, Konstantinos Varzos, described Theodore as an "energetic, resourceful, and exceedingly ambitious statesman, who inherited from his ancestor Alexios I Komnenos his endurance and persistence, but not the latter's intelligence, diplomacy, and ability to adapt".

Varzos furthermore points out that despite his great ability, Theodore's ambition to be the one to recover Constantinople and his irreconcilable rivalry with Nicaea actually hampered and delayed the restoration of the Byzantine Empire by several decades.