Let us take a step back from religious fervor for a moment and focus on the Anglo-Saxon kingdoms themselves.
The Heptarchy: Anglo-Saxon Ascendancy The first kingdom settled was Kent. To the north of Kent was Essex; to the south was Sussex; to the west was Wessex. (Get the idea?) North of Essex along the eastern coast of the Island was East Anglia. Directly west of East Anglia was Mercia. North of Mercia was Northumbria.
Kent was settled by Hengist and Horsa in the early 5th century. Oesc, Hengist’s son, succeeded to the throne and tightened his grip after the Britons abandoned Kent in 456. His son Octa succeeded him in the early 6th century. Oesc’s other son, Ethelbert, came to the throne in 560 and was named bretwalda, or overlord. By the time of the Synod of Whitby, Earconbert was on the throne.
Essex was founded about 500. Its first ruler was Ricola, son of Eormenric, Kentish king briefly in 560. Essex included London. Essex grew steadily, though it refused Church help for a time. The ruler at the time of the Synod of Whitby was Sigeberht II Sanctus.
Sussex, of course, was founded by Aelle in 477 and ruled by him for more than 40 years. He was the first bretwalda, so named in 540. After the death of Aelle, in 514, not much is known of Sussex until the mid-7th century.
East Anglia was founded in 520 by Wuffa. His grandson, Raedwald, ruled from 593 to 624 and was bretwalda. The king of East Anglia at the time of the Synod of Whitby was Aethelwold.
Wessex was founded in 519 by Cerdic, whose son Cynric is thought by some to have been the Saxon leader at the Battle of Badon Hill. Cynric’s son Ceaulin was bretwalda and was the leader of Wessex at the time of the Synod of Whitby.
Mercia was founded about 600 by the Iclingas. They became known as Mercians (Lords of the March) soon after. The first leader was Cearl, in 606. The leader of Mercia at the time of the Synod of Whitby was Oswiu of Northumbria.
Northumbria was the result of the fusing of two other kingdoms, Bernicia and Deira. “Northumbria” literally “People North of the Humber”–in other words, the Humber River. Ida was the first leader of Bernicia. Edwin of Deira, the son of Aelle, ruled both kingdoms from 616 to 632 and was bretwalda during this time. Oswald united the two kingdoms as Northumbria, beginning in 633. Oswiu succeeded him in 641, was named bretwalda, and was the leader of Northumbria at the time of the Synod of Whitby. In fact, it was Oswiu himself who made the fateful decision to choose the Roman church over the Celtic church.