The fact that the second-to-last chapter is focused on Buck's love for John Thornton highlights Buck’s: the choice between civilization and the wild
confusion about his identity
distrust of the world of men

Highlight all instances of parallel structure. there is no longer any room for hope. if we wish to be free—if we mean to preserve inviolate those inestimable privileges for which we have been so long contending—if we mean not basely to abandon the noble struggle in which we have been so long engaged, and which we have pledged ourselves never to abandon until the glorious object of our contest shall be obtained—we must fight!