British spelling, past tense of fanaticise; made fanatical or caused to become excessively devoted.
From 'fanaticise' plus the past tense marker -ed. This is the British variant spelling of 'fanaticized,' showing the consistent -ise/-ize difference in British versus American English conventions.
Historical accounts describe how entire populations got 'fanaticised' by charismatic leaders or religious movements, and the word choice itself reveals whether the author sees the conversion as positive (inspired) or negative (brainwashed).
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