Sentence:  Zealots," and withal, took upon them to be the saviours and preservers of the City, but as it prov'd, the hastners & <WSD>precipitators</WSD> of the destruction of that Kingdom ... 
Meaning of the word marked with <WSD> tags:  One who or that which precipitates (causes something to happen or urges it on with vehemence or rashness).