The idiom "围魏救赵" is formed through the direct concatenation of four characters: "围" (wéi, to besiege), "魏" (Wèi, the state of Wei), "救" (jiù, to rescue), and "赵" (Zhào, the state of Zhao). It derives from a specific historical event during the Warring States period where the military strategy involved besieging the state of Wei to compel the withdrawal of its forces from the state of Zhao, thereby achieving the rescue of Zhao. The characters sequentially narrate this action and its objective, encapsulating the tactic in a literal four-character structure.