Sentence:  It performed this task in the beginning and has always exercised the power of passing on books. By this transfer, the Pope points out, every danger of a collision, which might become very embarrassing, is evaded. The <WSD>prevention</WSD> of such collisions has indeed been one of the chief reasons for Pius X to undertake the complete reorganization of the Roman Curia. 
Meaning of the word marked with <WSD> tags:  The act of preventing or hindering; obstruction of action, access, or approach; thwarting.