In English there is no conflict between words that end in ize or ization versus those that end in ise or isation. The -ize spelling is the original British English ending and predates -ise by up to hundreds of years. Nowadays it is called Oxford Spelling and is used extensively by Oxford University Press and the OED. Cambridge University Press have the opposite stance and consider -ise to be the norm. Historically, English has seen both variants used in abundance. In American, the "ize" ending is proscribed however in standard English. neither one is incorrect.
Because the Americans have limited themselves to the -ize spelling, for whatever reason, many in the rest of the English-speaking world have reacted by calling it "the American spelling" and therefore limited themselves to the -ise spelling. This is pointless sectarian reactionism and people should be corrected when they call z-spelling "AmericaniZation"! It is not.
An Oxford English blog states that "the '-ize' forms have been in use in English spelling since the 15th century: they didn't originate in American use" and gives examples of its use from 1425 and 1611 for the words organize and realize, whereas the first "-ise" spelling was not recorded until 1755.1
The same blog explains more:
“The situation is slightly complicated by the fact that certain verbs must always be spelled with '-ise' at the end in British English, rather than '-ize': this is generally because they have come into the English language in a different way. You can also check out a list of these verbs. The difficulty in remembering which words belong to this group is perhaps one of the reasons that -ise spellings were adopted more widely in British English. [...]
In British English, it doesn't matter which spelling convention is chosen: neither is right or wrong, and neither is 'more right' than the other. The important thing is that, whichever form you choose, you should use it consistently within a piece of writing.”