That it affects around 200 verbs, see Upward, Christopher and Davidson, George. ("The suffix -IZE/-ISE" ), ''The History of English Spelling''. John Wiley & Sons, 2011, p. 220.〕 The suffix ''-ize'' has been in use in the UK since the 15th century,〔 and is the spelling variation used in American English. The belief that ''-ize'' is an exclusively American variant is incorrect.〔

〕 The OED lists the ''-ise'' form of words separately, as "a frequent spelling of -IZE...":

This practice probably began first in French; in modern French the suffix has become -iser, alike in words from Greek, as baptiser, évangéliser, organiser, and those formed after them from Latin, as civiliser, cicatriser, humaniser.
Hence, some have used the spelling -ise in English, as in French, for all these words, and some prefer -ise in words formed in French or English from Latin elements, retaining -ize for those formed from Greek elements.
But the suffix itself, whatever the element to which it is added, is in its origin the Greek -, Latin -izāre; and, as the pronunciation is also with z, there is no reason why in English the special French spelling should be followed, in opposition to that which is at once etymological and phonetic. In this Dictionary the termination is uniformly written -ize. (In the Greek --, the i was short, so originally in Latin, but the double consonant z (= dz, ts) made the syllable long; when the z became a simple consonant, /-idz/ became īz, whence English /-aɪz/.)