Why should we a priori state that large nations can't openly discuss and carefully plan acts of terrorism using the most modern weapons and tactics and spurious justifications?
We shouldn't, of course. The problem is large nations also have large communications systems and/or media control that perform all kinds of elaborate rhetorical gymnastics to avoid having their terroristic actions labeled as terrorism. Governments try to avoid the implication that they may be using the exact same tactics as their sworn enemies, even if the REASON for doing so is different.
In most situations, ambiguity is politically inconvenient.
But the application of a moral standard does not mean you have to apply a subjective religious standard. There are ethics based on harm reduction and rights promotion.
And yet, a terrorist attack for an ethical reason remains a terrorist attack. Tossing hand grenades at lynch mobs, for examples, would constitute a terrorist attack. Using a car bomb to assassinate another terrorist would be as well.
John Brown's attempt to foment a slave rebellion in the South was, arguably, a terrorist act.
The matter could be discussed. But slavery itself was such a huge act of terrorism, the institutionalization of terrorism with the consent of government, that John Brown's terrorism pales in perspective.
I don't believe it is impossible for a terrorist to become the victim of terrorism. Some people prefer to fight fire with fire.
If we look at harm reduction then we might say a lot of violence is justified if it is likely to end slavery.
Personally, I would say a lot of terrorism would be justified to end slavery. Certainly a campaign of random assassinations and/or bombings of the homes of slave owners could be justified morally, given that those owners were knowingly profiting off of a fundamentally immoral and despicable institution and were willing to start a war to preserve it.
If you want to avoid all the moral equivocation and rhetorical bullshit practiced by nation states, one is forced to conclude that terrorism in self defense is still terrorism.
The German use of V1 and V2 rockets against England, targeted almost entirely indiscriminately at civilian population centers, were intended to demoralize the population and break their will to fight; this is a DIRECT use of state terrorism against an enemy in a time of war.
If we talk about WWII then we must throw most so-called definitions of terrorism out the window since all sides deliberately attacked civilians as a war tactic.
Or we could just concede that the Allies employed large-scale terrorism as one of their battle tactics. The Axis powers unquestionably did; what's wrong with admitting the same of the Allies?
You give no reason we should not consider violent actions that terrorize and have no valid justification as acts of terrorism.
Because it is intent, NOT justification, that defines an act of terrorism.
The attack on Pearl Harbor, for example, caused massive dismay and panic in America and particularly in Honolulu where it was feared that the Japanese Army was about to physically invade them. That the attack terrorized the population, and being unprovoked, had no moral justification. Conversely, the attack on the RMS Lusitania would be considered a legitimate act of war since the vessel was believed to be carrying war materials to England, thus making it a legitimate target.
Justification does not and should not factor into that definition. If you intend to terrorize the population with your actions, then you are a terrorist. If your target possesses what appears to be valid military value to your enemy, then it isn't an act of terrorism even if striking it scares the hell out of the population. The only real problem with this is that intent is sometimes hard to prove, but it can be demonstrated by examining what the attackers actually knew about their target vs. what they stated/fabricated after the fact. An attacker who knows his target has no legitimate military value and blows it up anyway is almost certainly a terrorist. An attacker who hits what he thinks is a military target and then turns out to be tragically wrong is not. An attacker who doesn't know or care if a target has military value is very likely a terrorist as well.