Reddit reviews The Meaning of Everything: The Story of the Oxford English Dictionary

' Just ranting a bit further, because the reasons behind some this stuff are actually rather interesting (at least to me):

The notion that states all have prideful and unique language rules is bonkers.

Regional spoken dialects and accents slowly morph over huge swaths of land that don't know state boundaries. The only place you see a strong local difference are in very large cities, and even then, they're just more exaggerated versions of what are already regional ways of speaking. They're also never drastic enough to be unintelligible to anyone. Again, all of this is moot in the sense that written American English is completely standardized. Textbooks are usually written by staff writers from a few international publishers who have a virtual monopoly on the market, not by individual states. Though some states do sometimes by law make certain requirements to the publishers, they're not making their own rules about English, but rather much more awful things, like whether or not the Bible is science.

We say "healthy" instead of "healthful", but not because some state made-up their own rules and confused the textbooks nor because we're ignorant or lazy regarding the differences in usage or meaning in other places.

This can be traced back to the creation of the Webster's Dictionary.

Up until the mid 19th Century, there really was no notion of "proper" or definitive spelling of English in any country. The Oxford English Dictionary, in competition with several others, was created in an attempt to finally make a standard. Others made their own, with different spellings and definitions. This is a great book about its creation. Over here in America, Noah Webster also thought this was something needed. However, the problem was that people simply no longer spoke the way they did in England. Suddenly asking everyone to standardize on contemporary British English would be like asking people (who didn't travel as much or have television or radio back then) to speak a language they'd never spoken and likely never heard. Such standards would be both dishonest and nonfunctional. So he set about making his own spellings and definitions that he felt accurately reflected the American usage. Now Americans could also benefit from having a standard, though an accurate one, rather than one that would have been foreign and artificially imposed. For the lands of the British Empire though, British English followed them.

In the end, there are incredibly few grammatical differences between American English and British English. The real differences are in vocabulary and spelling, which was changed to reflect pronunciation, at a time when England itself didn't have official or proper spellings quite worked-out yet. The only reason Australia's isn't more unique from England's is that when people first started standardizing these things they pretty much were England (and its prisoners). If Australia had been an independent commonwealth with several hundred years of unique colonial culture at the time people got down to standardizing, I imagine you also would have made some local spellings and usages.