>no war can be won by defense alone
If so, how do you win an insurgency type of war? After the initial destruction of a weaker country's armed forces you'd need to occupy the land, otherwise the early victories would be for naught. Yet when you do that, you turn to defending instead of attacking, thus giving momentum to an insurgency.
Is the only feasible strategy to rely on local infighting / creating loyalists out of locals, while your armed forces would only strike from afar? Worked with Yugoslavia.