It shouldn't take years of pre-emptive diplomacy just to enforce the status quo. Did the Brits, French, Prussians and Austrians all invest a massive amount of influence in Belgium in 1839 just to be able to guarantee it?
I don't know why people keep talking about "years" needed to get friend status. It doesn't take that long unless you are competing with 4 GPs in China or something similar.
Your Belgium example is even worse. First, if you share a border and are on the same continent, it takes even less effort to build up influence. It's like shooting diplomatic fish in a barrel. Second, you can build influence even when the target is at war with another power. So, in your Belgium example, most GPs managed to build up to Friend during the civil war. And whether or not the war is new or old, the moment you hit Friend, you can intervene. So, in Vic2 mechanics, GPs that felt an independent Belgium was in their interest (GB, Prussia, Austria) started building influence. The moment it was independent, this became possible. Within a span of time, Belgium was still independent, so the relevant GPs had enough influence to threaten intervention. I should point out here that the possibility of French annexation is one reason these GPs all had an interest in influencing Belgium and keeping them neutral. And since France was not about to have a hostile state on its border, they got into the act, too.
The Treaty of London is also an example of Friend status at work. Having Belgium be at Friend status with the GP signatories to the treaty effectively is the same thing as all of them guaranteeing Belgian independence.
If you want to argue that GPs can't influence revolutionary movements, meaning you can't get influence on a rebellion before it forms an actual country, I agree. EU3 is better about this, in that you can help rebels and their new state will be friendly to you. Furthermore, if you want to argue that the AI does not predict the best countries in which to put its influence to stop imperialism, then I might also agree. Humans are a lot better at saying, "Hey, I better Friend Japan to prevent those jerks over in GPisstan from grabbing them while they are unciv." But I find it bizarre that anyone thinks you should automatically be able to intervene in all wars, all the time. Russia and GB have interests in Afghanistan, represented by their influence (hell, the article on Wikipedia is entitled "
European Influence in Afghanistan"). Why should Prussia, with no influence in Afghanistan, intervene if GB or Russia invades? If you have no influence in the region, you don't get to play unless your allies ask you to get involved. Do not pass go, do not collect intervention wars without a reason.
EDIT: I would tend to agree, Celdur, but since terms like "unciv" and whatnot reflect the attitudes of the power brokers in charge of GPs, and are not necessarily an accurate reflection of what's really going on in an area, the real question isn't whether SA countries were "uncviilized." It matters how they were perceived. Given their treatment at the hands of Europeans in the period, they were not considered the same as China, Persia, Siam, and so forth. It would also break the game if you could use unciv CBs to crush them.