trigger

There are fears that the incident may be a trigger for more violence in the capital.

有人擔心，這次事件可能在首都引發進一步的暴力活動。

https://dictionary.cambridge.org/zht/%E8%A9%9E%E5%85%B8/%E8%8B%B1%E8%AA%9E-%E6%BC%A2%E8%AA%9E-%E7%B9%81%E9%AB%94/trigger

https://hk.lifestyle.appledaily.com/lifestyle/columnist/2459936/daily/article/20090620/12899180