Everyone is taking the serious, grounded approach. I'll go for the fantastical approach.
It really depends on consequences, finality, and degree of collateral damage involved. In other words, it depends on the setting.
If you have a world where the lives of people aren't actually endangered, like a VRMMO, you end up with war rhetoric, and also end up with easier 'noble' justifications for war. When you strip riches and life from the equation, you end up with people picking fights for ideological reasons, and dont have to deal with too much of the negative baggage.
There's other ways you can draw up a noble war. Imagine a scenario where you have a necromancer in a closed off country. This guy has no intention of ever leaving his country, but he's populated it with undead. It wouldn't be hard to call something "noble" if the attacking side gets involved to to prevent, say, further defilement of the soul, as according to their beliefs.
Someone else mentioned a war to stop a country from committing evil to its people. You could play that kind of thing up and just create a totally evil empire, where going to war with them is justified.
So, in the world of fiction, yes. 100% anyone can force noble wars if they're clever with covering their bases. I do think you need REALLY black and white situations to make it work though.
The more nuanced the sides get, the less noble it becomes, and the more the 'noble' side needs to argue for why they're right