Progressive War is a military term encompassing a military strategy where only enemy combatants are targeted and civilian collateral damage and casualties are kept to a minimum. The principles for Progressive War were established by Dutch jurist Hugo Grotius who is consider a founder of international law in his book De jure belli ac pacis libri tres(On the Law of War and Peace: Three books) published in 1625. A successful practitioner of Progressive War was Helmuth von Moltke the Elder as chief of staff of the Prussian Army in the nineteenth century.
The obverse to Progressive War is Unlimited War which includes civilian populations as legitimate targets. The aim of Unlimited War is to use military action against civilians in the hope of undermining the populations will to fight, to undermine their support of their leaders and thereby influence the policies of those leaders to continue the conflict. Examples of Unlimited War is evident in the use of cluster bombs, the bombing of Dresden in World War II, the German bombing of London among many other examples.
The philosophy of Unlimited War is controversial. Many consider it a form of terrorism, in the sense of deliberately attacking civilians in the hope of changing their mindset. Such ambiguities between Unlimited Warfare and terrorist strategies could be the source of why many terrorist groups consider themselves soldiers, and many label American military forces terrorists.
Guerrilla warfare can be considered Progressive if only enemy combatants are targeted, but becomes terrorism when civilians are targeted.