American English was built by collision, not by a single origin

Bryson's foundational argument is that the language spoken in America never developed as a simple continuation of British English transplanted intact across the Atlantic; instead, it emerged from constant collision and blending between the dialects of different English-speaking settlers, Indigenous languages already spoken on the continent, and later the languages of enslaved Africans and successive immigrant waves.

He traces how early colonists, often from different regions of Britain with their own distinct dialects, found their speech patterns mixing and leveling out as they settled together in new communities, producing forms of English that diverged from any single regional British source relatively quickly. This process didn't stop once; it simply kept happening as new groups arrived.

His broader point is that treating American English as a corruption or simplification of a purer British original misunderstands the actual mechanism: it was never one thing being watered down, but many things constantly combining into something new.

*Takeaway: language variation isn't decline from a purer original — it's the ordinary, ongoing result of different speech communities mixing.