Sentence:  With the aim of moving toward our subsequent discussion of the <WSD>driving forces</WSD> behind mass indebtedness, however, we might take things a little further by condensing the original work's detailed breakdown into two very broad causes of individual indebtedness. 
Meaning of the word marked with <WSD> tags:  Impetus; a person or thing that causes, stimulates, or motivates something to happen.