You can’t experiment with single variables that weren’t within the range of the technology or the culture of the times. Within these limits, though, counterfactual reasoning can help to establish chains of causation: to argue that the Japanese might not have attacked Pearl Harbor if the American oil embargo hadn’t been imposed; or to claim that the Americans might not have chosen to cut off the oil flow if the Japanese hadn’t moved into French Indochina—these are perfectly legitimate positions for historians to take.
