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?
The rest of the sentence explains it:
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:
(Herodotus, Histories 1.106)