driving force
noun[C,usually singular]
ukussomeone or something that has thepowerto make thingshappen:
a driving force behind/for/in sthTheexplosioninstockmarketwealthhas been animportantdrivingforcebehindconsumerspending.
Trade is thedrivingforceforsustainedeconomicprosperity.
Women aredefinitelyadrivingforcein theindustry, she said.