to set off, trigger

触発(しょくはつ)	To trigger a controversy, war, or to catalyze a chemical reaction. Not necessarily intentional.

しげき	To intentionally provoke someone or something. Not always bad – you can stimulate a baby by tickling it, or stimulate a patient with electrodes.

しょうらい	A very literary word which you don’t have to worry about.

引金(ひきがね)	Is literally a trigger, but I’ve seen it used as a metaphor too.