Sentence:  The weekly loss is partly counterbalanced by 500 arrivals each week from West Germany , but the hard truth , says Crossman , is that `` The <WSD>closing</WSD> off of East Berlin without interference from the West and with the use only of East German , as distinct from Russian , troops was a major Communist victory , which dealt West Berlin a deadly , possibly a fatal , blow . 
Meaning of the word marked with <WSD> tags:  the act of isolating something; setting something apart from others