I �m afraid I studied both history of English and history of German in pre-Internet days, so I don �t have those references anymore. However, as a quick overview of what I remember of philology, English is part of the Germanic branch of the Indo-European family of languages. It is historically a close relative of German and Dutch, although the closest living language relative of English is Frisian.

 

You can see the relationship most clearly in Old English, such as that of Beowulf. (If you want to see for yourself, I recommend Seamus Heaney �s translation. Old English is on even pages; his Modern English is on odd pages.) Modern English and Modern German, though, have very different grammars. This is a result of the occupation of England for many years by the French as a result of the Battle of Hastings in 1066. I have never seen any scholastic research about this, but it is my personal belief that the French occupation of England turned English into a creolized language, with simplified grammar. It also resulted in English having a heavily romanticized vocabulary. Even today, though, most of the very common words in English trace back to Germanic roots. I �ll just mention the Great Vowel Shift of the late 1500s and early 1600s in passing, since you �re more interested in earlier history.

 

Other contributors to this site may know more than I do.

You may find some valuable information concerning English language history  by following this link:

http://homes.chass.utoronto.ca/~cpercy/helhome.htm

Hope it helps you.