Sentence:  `` They are determined '' , Montgomery writes , `` not to be surprised again , and now insist on a state of readiness for war which is not only unnecessary , but also creates nervousness among other nations in the Western Alliance - not to mention such great suspicions among the nations of the Eastern bloc that any progress towards peaceful coexistence or disarmament <WSD>is</WSD> not possible '' . 
Meaning of the word marked with <WSD> tags:  have the quality of being; (copula, used with an adjective or a predicate noun)