The difference is that education is now ubiquitous and almost everyone who matters is literate. The reason why Latin diverged into Romance languages is that lit

The difference is that education is now ubiquitous and almost everyone who matters is literate. The reason why Latin diverged into Romance languages is that literacy among the secular class died out, and both the elite and the peasants had no knowledge of formal Latin. (The Church did, but it was relatively weak in Early Middle Ages, certainly not strong enough to push the society to use a certain standard of language.) Sure, if the educational system today collapses and we revert to pre-industrial state like around 500 AD, English will spontaneously develop into a family of mutually unintelligible languages. I sincerely hope that this won't happen, though, because 95 per cent of humanity would die. We cannot feed 8 billion people with pre-modern technology.