The driving force or idea behind something that happens or is done is the main thing that has a strong effect on it and makes it happen or be done in a particular way. 起推动作用的
adjective [原级]推动的,强有力的;猛烈的,倾泻而下的
Consumer spending was the driving force behind the economic growth in the summer. 消费者支出是夏季经济增长背后的推动力。