It's war time again, and that means the inevitable attempts by both sides to paint themselves as the holy defenders beating back the barbarian aggressor hordes. That makes it a good time to look at aggression and defence in an objective fashion.
First, let's make clear that there two different concepts here. There is the concept of aggression versus defence, and the concept of a justified or unjustified war ('valid CB' or 'invalid CB'). In this case, Ragnarok's CB is cast iron: a government official deliberately and knowingly aiding an enemy after being warned not to do so is the best CB of any war for some time. This is not a note about the CB, but about what it actually means to be the aggressor.
There is a longstanding precedent that being provoked into a war doesn't make you the defender. The most obvious recent example is Karma, where NPO is almost universally considered to be the aggressor, despite their rather feeble attempts to justify it based on OV accepting screenshots. That situation is perhaps a little different in that they did not manage to prove that OV had committed 'acts of war' as so considered by most alliances, but no-one outside their immediate circle of friends would consider that anything other than aggressive. (And because OV couldn't be shown to have done anything seriously wrong, unjustified aggression at that, which is why so many alliances joined together to fight them at that moment.)
Another approach to the argument is to point out that 'acts of war' – aid and in-game spying – do not actually put you in a state of war at all. It's therefore non-sensical to claim that such acts immediate put you in a state of defensive war – if you don't choose to start a war over them, there is no war at all, so how can it be defensive. With spying this is particularly true as many spy ops are not even revealed, so they clearly don't start a war because you don't even know who you're supposedly fighting! You can test this by aiding a rogue nation and observing how it doesn't immediately put you at war with the alliance upon which the rogue is going rogue, though you should expect to pay reparations for such an experiment.
Let's take a look at a document which was well respected for a long time, and which actually defined the concept of 'aggression', the Citadel treaty:
Direct Aggression: Actual or attempted military action or economic sanctions by a party against a second party, except in the following circumstances:
1. When the first party is responding to military action or unjustified economic sanctions initiated on them by the second party; or,
2. When the first party is responding due to the activation of a mutual defense clause with a third party where the second party initiated military action or unjustified economic sanctions upon said third party.
3. Actual or attempted acts of espionage.
[OOC: Note that the Lux Aeterna was written before in-game spying. Espionage doesn't mean that.]
It's one of the very few documents to actually make a stab at defining aggression and defence for legal purposes, and as far as I'm aware no-one ever challenged these definitions. In less lawyerly terms, it means that you are acting aggressively if you start a war unless (i) someone attacked you, (ii) you are activating an MDP or (iii) someone is (out of game, i.e. forum) spying on you. The addition of that third clause is interesting in itself, as in general spying is considered to be a solid CB but not in itself aggression, and in point of fact Citadel did not actually follow that clause when TOP was spied upon by Vox (Grämlins, FCC and Umbrella did not declare war on Vox). However, forum spying is so rare these days (everyone realises how dumb it is) that the presence of the espionage clause can be considered an interesting anomaly and is not directly relevant. What is clear is that being provoked into a war by words (TOP/IRON in Bipolar) or aid (RoK here) relieves you from being aggressors.
Another place to look is the labyrinthine legalities of OBR treaties. For example, in their MDP with GR, we find this exception to defensive obligations:
... with the exception of any conflict where the it is as a result of a declaration of war by either ally or as a result of other treaty obligations. No obligation exist in either of these cases.
The second part of that is a standard non-chaining clause, but the first defines 'aggression' in the context of the treaty, and a declaration of war is considered aggressive (i.e. voids the defensive obligation) whatever justification it may have.
(In the Writ de Credo one can find a very broad definition of 'hostility', but that treaty was, as we now know, drafted as a legal trap and its definitions chosen accordingly.)
So we can see from three separate approaches – precedent, logic and well regarded legal documentation – that what counts as aggression is being the first ones to start the war. It can become blurred later in a war (for example is all of Karma defensive? or just the alliances which were attacked and their MDP partners?), but at the outset it is clear: the alliances which start the war (NPO in Karma, NpO in Bipolar, and RoK/GOD/R&R/VE here) are aggressors, and their immediate targets (OV, \m/ or NSO) are defenders.
A final reminder that this is not a post about justification. It is possible to be a justified aggressor; a good example from history would be the attack on Golden Sabres for supporting FAN's senator during the FAN war. In this case that is unusually clear-cut because of NSO's willingness to put their alliance in a dangerous position (taking in active rogues) that others wouldn't.