Written by Dyami Millarson
Modern English is descended from Middle English, which is descended chiefly from the Mercian variety of Old English. There were four main varieties of Old English: Mercian, West Saxon, Kentish and Northumbrian. The most dominant tongue at the time was West Saxon and therefore a great part of the Old English literature is written in West Saxon. It is, therefore, intriguing that Modern English and Middle English are descended from Mercian rather than West Saxon.
Modern English and Middle English are so different from all vatieties of Old English that a modern English reader could not understand an Old English text but could understand a Middle English text with some extra effort. This is why Old English is also simply called Anglo-Saxon. Although the direct ancestor of English, it is quite a different language from English.
Anglo-Saxon is derived from Anglo-Frisian, which was the common Ancient Frisian language of the Angles and the Frisians (Teutonic tribes that originate from the Wadden Sea region of the European mainland). At one point, the speakers of Anglo-Frisian migrated to Britain and their language changed to Anglo-Saxon over time due to the loss of contact with other Anglo-Frisian speakers. The isolation that arose from the geographical distance between Britain and mainland Europe was the main culprit for the linguistic split between the speakers of Anglo-Frisian.
When one thinks about it, one may compare it to the later linguistic situation between American English and British English. The Frisians remained on the old continent and continued speaking Ancient Frisian, which evolved into Old Frisian, but the Angles had moved and started speaking Anglo-Saxon after their Ancient Frisian language had gone its own way and thus could no longer be considered Anglo-Frisian proper. There must have been a time when one spoke ‘European Continental Frisian’ and the other spoke ‘British Insular Frisian’.