In the year 409 the inhabitants of the former Roman diocese of Britannia (that's Britain to you and me) rebelled against their former Roman masters, and declared their independence. This self government lasted a generation or more before it broke down in the face of the revolt of some of the Germanic mercenaries hired to protect the island and the influx of fresh Germanic insurgents from the continent. (See Sub-Roman Britain for further details of this confused and ill-documented period of British history.)
And so it came to pass that a a rag-bag of former mercenaries, pirates and sundry warlords of Germanic origin ended up on the shores of Britain all engaged in the business of looting, pillaging, fighting local Romano-British rulers (and each other) and seeking to establish for themselves their own little kingdoms. In the process of which they stopped being Germanic and became Englisc or Anglo-Saxons as we prefer to call them today to avoid confusion with the post-1066 Frenchified English.
Many of these 'Anglo-Saxon' kingdoms were comparatively short lived, and existed only for a generation or two in the fifth and sixth centuries; some now exist in name only, some are known only for a short list of kings, and most were swallowed up or relegated to the status of sub-kingdom by one of the 'big three', that is Northumbria, Mercia and Wessex.
Northumbria made the early running, expanding at the expense of its Brythonic neighbours and reaching the peak of its power in the late seventh century; Mercia became the dominant power in the eighth century and Wessex vied to keep up. Which one of these three would have eventually won the race to domonate the island of Britain is uncertain, in the end the contest was decided by the Vikings who conquered Northumbria, fatally weakened Mercia and left Wessex to inherit the prize on the basis of the last man standing.
The Everything list of Anglo-Saxon kingdoms
And as you will see, there are a lot more than seven, therefore laying to rest that hoary old myth of the Anglo-Saxon Heptarchy.
- Bernicia - named after the former Brythonic kingdom of Bryneich based on the fortress of Bamburgh, united in the early seventh century with Deira to form Northumbria
- Ciltern Saetan - The kingdom of the Chiltern Saxons
- Deira - named after the former Brythonic kingdom of Deywr, roughly modern Humberside, swallowed up by Bernicia to form Northumbria
- East Anglia - The kingdom of the East Angles, roughly the modern counties of Norfolk and Suffolk, had a brief period of dominance in the early seventh century before falling under the sway of Mercia
- Essex - The kingdom of the East Saxons to the north of the Thames estuary, retained in its own kings until the early ninth but century but probably subject to Mercia or Wessex for most of its history
- Gewissae - Early Germanic kingdom of uncertain origin in the fifth century based in the Thames Valley; a forerunner of the later Wessex
- Hwicce - Centered on Gloucester a sub-kingdom variously under the domination of Mercia and Wessex
- Iclinga - A little known early Anglian kingdom in the Midlands, a forerunner of Mercia
- Isle Of Wight - a Jutish kingdom eventually swallowed up by the emergent Wessex
- Kent - The Cantware the earliest Anglo-Saxon kingdom named after the former Brythonic kingdom of Ceint, reduced the status of a sub-kingdom of Mercia and Wessex at different times but retained a measure of quasi-independence until the mid ninth century
- Lindsey - The kingdom of the Lindiswara based around Lincoln
- Magonset - Based on the Kentchester or Roman Magnis a sub-kingdom of Mercia
- Mercia - Also known as the kingdom of Southumbria, the Angles south of the Humber. Emerged in the early seventh century, dominated in the eighth and virtually wiped out in the ninth by the Vikings
- Middlesex - The kingdom of the Middle Saxons; no details of any kings have been retained and seems to have been a sub-kingdom of Essex
- Surrey - The kingdom of the South Ridge; variously a sub-kingdom of Mercia and Wessex
- Sussex - The kingdom of the South Saxons, reputedly founded by Aelle leader of the Germanic insurgents in the late fifth century, but then drops out of recorded history until swallowed by Wessex in the late seventh century
- Northumbria - The kingdom of the Angles north of the Humber, which arose out of the amalgamation of Bernicia and Deira and was further enhanced by the conquest of neighbouring Brythonic kingdoms of Rheged, Elfed and Gododdin. Started a gradual decline in eighth century, conquered by the Vikings in the ninth and replaced by Jorvik
- Wessex - The kingdom of the West Saxons, that appeared in the late seventh century
- Wrocenset - Based on modern Wroxeter or Roman Viroconium, probably a sub-kingdom of Mercia
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