Sentence:  In each of the last , the trial marked the beginning of a new course : in Moscow the liquidation of the Old Bolsheviks and the <WSD>tightening</WSD> of Stalin 's dictatorship ; in the United States the initiation of militant anti Communism , with the repentant ex Communist in the vanguard . 
Meaning of the word marked with <WSD> tags:  the act of making something tighter