Why does Oxford, as in the old SOD, list words ending in -ise as variants of the same word spelt with -ize?

ECONOMIST: Johnson

The hotel clerk took pity on me, pointing out that in Hindi, the word for tomorrow is the same as the word for yesterday.

BBC: India��s chaotic lesson in letting go

Sixth, let us show by our willingness to bring Turkey, a proud Muslim nation into the EU on the same and equal terms as all others, that Europe is committed not just in word but in deed to a Europe of diverse races, cultures and religions all bound together by common rules and a sense of human solidarity and mutual respect.

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