Hmm, tbh in Crimean War reason would be even more serious - russia practically taking away sovereignty of a major power (Ottomans) holding a significant part of Europe and world's most strategic waterways.
I dont have an issue about general european war breaking out bcz of a small or weak but strategic country in europe. I have an issue with single european great power starting a bloodbath in europe to defend a tiny colonial nation. And its concerning bcz if it happens once, it can happen thirty times - welcome to vic2's 17th great war
For what I thought I knew, Russian invasion (trying really hard not to think of present day concerns) was the "second act" of a diplomatic conflict raised around the protection of Orthodox minorities. And even if this is a bogus, fabricated casus belli, it is still a minor issue. But as I said in another post, history is not my strongest point so I am more than happy to stand corrected.
Also, I think that we advocate a similar point concerning the need of limiting the possibility of getting into full-fledged world war's for each minor conflict.
However, I differ on you on the idea of making it impossible for colonial wars to escalate into Great, if not world-wide, wars. The justification for that would not be history, but plausible alt-history.
Imagine a case in which Prussia and France have an already highly degraded relation, with several areas of border friction, conflicting interests. When France decides to colonise Tibesti, winds of war have been already blowing for quite a while. Then, say that Tibesti is in a region where Prussia has a genuine interest due to the presence of a discoverable resource that could be strategic, or because it is essential to establish a land bridge between Prussian Equatorial Africa and Prussian Libya, or for whatever other strategic reason.
Would that be so inconceivable for Prussia to seize the occasion to start a war to "cut France to size" and protect his strategic interests at the same time? Especially if Tibesti promised a piece of Alsace to Prussia during the negotiation phases.
And there, you have the Franco-Prussian wars of 1970, only started under the pretext of preventing the colonisation of a mountainous region in Africa.