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Actually, the current vogue for claiming that British spellings are all "-ise" is only about 20 years old.
The Oxford English Dictionary still gives "-ize" as the preferred spelling, with "-ise" as the variant.
The problem lies in the fact that while most English words of this type were spelled "ize", but it didn't matter if they were spelled "-ise", there was a small list of exceptions that were NEVER to be spelled "ize" (because of their etymological origin).
The rule of thumb came into being that if you were in doubt, it was better to use "ise" than "ize". And so the variation became enshrined, just around the time when computer spell-checkers came into being.
There's an episode of the TV detective show "Morse" from the 80s, where he thinks a suicide note is false because "no Oxford man would spell 'realize' with an S."
Most American spellings are ones that used to be common in the UK in the 18th and 9th centuries.
So let's have no "You're wrong" type comments from either side, thanks.
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