"Fight with the grape": what does it mean?

I am reading Why the West rules---for now and found the idiom "to fight with the grape":

Like the Medes before him, he fought with the grape: he let the Massagetan vanguard loot his camp [...]

I just did not get it. What does it mean?

Solution 1:

The rest of the sentence explains it:

Like the Medes before him, he fought with the grape: he let the Massagetan vanguard loot his camp, and when they were drunk, slaughtered them and captured their queen's son.

The grape in question is that used to produce wine. The idiom refers to the tactical use of alcohol, and the bit about the Medes refers to these events:

At last Cyaxares and the Medes invited the greater number of the Scythians to a banquet, at which they made them drunk and murdered them, and in this way recovered their former power and dominion.

(Herodotus, Histories 1.106)