serve as the driving force

serve as the driving force (behind someone or something)

To act as the instigator, catalyst, or motivator that compels someone to do something or causes something to happen. While they haven't admitted why they reversed their decision, everyone knows the lawsuit served as the driving factor. The willingness of the banks to let anyone and everyone get a mortgage, whether or not they would be able to meet their repayments, served as the single biggest driving factor behind the financial crisis. My family has always served as the driving factor behind me.
See also: driving, force, serve, someone
Farlex Dictionary of Idioms.

serve as the driving force

(behind someone or something) Go to the driving force (behind someone or something).
See also: driving, force, serve
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs.
See also:
  • a crack at (someone or something)
  • (someone or something) promises well
  • a/the feel of (something)
  • (I) wouldn't (do something) if I were you
  • (have) got something going (with someone)
  • a straw will show which way the wind blows
  • accompanied by
  • accompanied by (someone or something)
  • accompany
  • (there's) no fear of (something)