Sentence:  It was because of this chain-reaction as much as for any other <WSD>reason</WSD> - that is , because of the growing independence of the planar unit in collage as a shape - that the identity of depicted objects , or at least parts of them , re-emerged in Braque 's and Picasso 's papiers colles and continued to remain more conspicuous there - but only as flattened silhouettes - than in any of their paintings done wholly in oil before the end of 1913 . 
Meaning of the word marked with <WSD> tags:  a rational motive for a belief or action