drive a wedge between

separate

分開，隔離

the general aimed to drive a wedge between the city and its northern defences.

將軍打算把該城和它北部的防御工事切斷。

thin end of the wedge

(informal)an action or procedure of little importance in itself, but likely to lead to more serious developments

(非正式)可能引起大變化的小事