Sentence:  The only contrary action , in the future as in the past , runs the risk of war ; and , now and in the future unlike in the past , any attempt to <WSD>repel</WSD> injury and to preserve any particular civilized attainment of mankind or its provisional justice runs some risk of nuclear warfare and the danger that an effect of it will , by human action , render this planet less habitable by the human race . 
Meaning of the word marked with <WSD> tags:  cause to move back by force or influence