"Driving force behind" is a powerful expression used to indicate the main reason or motivation for something. However, there are several synonyms that can be used in its place. For instance, "catalyst," "impetus," and "motivator" all convey the idea of something that initiates action or development. "Incentive," "stimulus," and "spur" are other synonyms that imply a driving force, particularly in terms of a reward or inspiration. Additionally, "propellant," "instigator," and "mover and shaker" are synonyms that highlight the forceful and dynamic nature of the driving force, indicating that it has the power to create change and movement.