which foreign power invaded it ?
Avars and their Slavic allies
Epirus
 Avars and their Slavic allies.
who was theodore komnenos doukas ? Ruler of Epirus and Thessaly what is the origin of the former name? "Mainland" or "terra firma" which mountains lie here? Pindus Mountains, Mount Smolikas, Tymfi etc.
wiki:11550710
Epirus [SEP] Epirus from the Slavic invasions until 1204
In the late 6th century, much of Greece, including Epirus, fell under the control of the Avars and their Slavic allies. This is placed by the "Chronicle of Monemvasia" in the year 587, and is further corroborated by evidence that several sees were abandoned by their bishops by 591. Thus in the bishop, clergy and people of Euroea fled their city, carrying with them the relics of their patron saint, St. Donatus, to Cassiope in Corfu. Of the various Slavic tribes, only the Baiounitai, first attested , are known by name, giving their name to their region of settlement: "Vagenetia".