King Æthelbald of Mercia is murdered in a palace coup and briefly succeeded by one Beornred, who is in turn ousted by Æthelbald's distant cousin Offa – King Sigeberht of Wessex is driven from power in favour of Cynewulf
King Eadberht of Northumbria abdicates in favour of his son Oswulf – King Cynewulf of Wessex takes Berkshire from Mercia and launches a war against the Welsh
King Oswulf of Northumbria is murdered – A severe winter strikes England
Construction of Offa's Dyke is said to have begun, a large linear earthwork of some 240 kilometres along the border of Mercia and the Welsh kingdoms, although this is challenged by more recent research which places construction sometime in the 5th century
Offa of Mercia conquers and subjugates Kent
Offa of Mercia subjugates Sussex
King Egbert II of Kent defeats the Mercian army of Offa at the Battle of Otford, taking the kingship of Kent
Offa of Mercia defeats Cynewulf of Wessex at the Battle of Bensington – Charlemagne writes Offa a letter
Offa retakes Kent and drives out his rival Egbert II
Cynewulf of Wessex is killed – Offa supports Beorhtric as new king of Wessex
Offa of Mercia and Beorhtric of Wessex call the Synod of Chelsea in Kent – Offa persuades the Papacy to make Lichfield the seat of an archbishopric – Offa makes the archbishop of Lichfield crown his son Ecgfrith as king of Mercia to secure the succession
King Ælfwald of Northumbria is murdered
Beorhtric of Wessex marries the daughter of Offa of Mercia, allying Wessex to Mercia – Vikings first appear and raid Portland, as recorded in the Anglo-Saxon Chronicle
The Anglo-Saxon scholar and clergyman Alcuin returns to the British Isles after an extended stay at the court of Charlemagne – King Æthelred I returns to Northumbria after 11 years of exile – Offa of Mercia takes control of East Anglia
Æthelred of Northumbria marries the daughter of Offa of Mercia, allying Northumbria with Mercia – Offa prepares coastal defenses against Viking attacks
8 June: Vikings raid the Northumbrian coast and sack the monastery of Lindisfarne, the first Viking attack on a monastery in the British Isles
King Æthelberht II of East Anglia visits the Mercian court but is killed by order of Offa – The Vikings destroy Monkwearmouth and Jarrow
Offa of Mercia receives gifts from Charlemagne – Offa refounds St. Albans Abbey
Æthelred of Northumbria is murdered, plunging the kingdom into chaos – Offa of Mercia and Charlemagne make a trading agreement – Offa dies after a reign of 39 years during which he subjugated Kent, Essex, Sussex and East Anglia (Mercian Supremacy) – Offa is buried at Bedford
Welsh attacks on Mercia
King Coenwulf of Mercia invades Gwynedd and also defeats Kent – Battle of Billington: king Eardwulf of Northumbria avenges the murder of former king Æthelred
Eardwulf of Northumbria invades Mercia
King Beorhtric of Wessex dies of poison and is succeeded by Egbert
About coastlines, please check the Wash, the Humber and the Glastonbury areas.
People usually don't understand the link between Glastonbury and the King Arthur legends, as Glastonbury hill could be Camelot or the Isle of Avalon. But why the "Isle" of Avalon as there is no sea? Just because there was at a time.
Of course, this it out of your map range, but...
Yea, I realise the coastlines here are the current ones rather than the historical ones, in the areas you mention. I think I made the mistake of drawing the coastline based on the modern one, thinking it would be fine, and then found out some areas were further inland in the 800's. And then I didn't feel like redrawing it... I made this map last year. ^^
A lesson learned for future maps: first check for obvious historical changes in the coastline, then draw it - not the other way around, haha. ^^
We all have our part of lazyness somehow...
Btw, in your "The Assyrian Empire, 934 - 612 BC" map, if you corrected the shores in the today Basra area, you located Troy inland...
You live in a country which is World #1 about sea shores and rivers management.