VaFunkoolo:
'ethnic' influence
Vikings - words such of "both", "window", "berserk".
Norman - loads of Old French words and influence on grammar, possibly one of the main reasons we have such a reduced case system.
Latin and Greek - everyone has borrowed something from Latin, Greek or Greek via Latin
Dutch - had an influence for a while
French - everyone borrowed from early modern French, especially English
Indian languages - we've pinched a few of their words
Caribbean English - more influence
American English - this is unavoidable
All the others I didn't mention (there are many).
They all add to the richness and diversity of the language. Not being so stuck on linguistic "purity" as in some languages, we adapt to these changes. It's just that some things grate on the ears.
But how do we borrow these new things in the langauge. Some are fed to us by advertisers, others we just pick up from music, films, or just being modern cosmopolitan people.