From Wikipedia

History of English

English is a West Germanic language that originated from the Anglo-Frisian dialects brought to Britain by Germanic invaders from various parts of what is now northwest Germany and the Netherlands. Initially, Old English was a diverse group of dialects, reflecting the varied origins of the Anglo-Saxon kingdoms of England. One of these dialects, Late West Saxon, eventually came to dominate.

The original Old English language was then influenced by two further waves of invasion: the first by speakers of the Scandinavian branch of the Germanic language family, who conquered and colonized parts of Britain in the 8th and 9th centuries; the second by the Normans in the 11th century, who spoke Old Norman and ultimately developed an English variety of this called Anglo-Norman. These two invasions caused English to become "mixed" to some degree.

Cohabitation with the Scandinavians resulted in a significant grammatical simplification and lexical enrichment of the Anglo-Frisian core of English; the later Norman occupation led to the grafting onto that Germanic core of a more elaborate layer of words from the Romance languages (Latin-based languages). This Norman influence entered English largely through the courts and government. Thus, English developed into a "borrowing" language of great flexibility, resulting in an enormous and varied vocabulary.