I'm truly ashamed not to have read any book on this subject, and i still can't defend the point of view of the south, but even the north is wrong overall. If they want to be united, it would benefit both sides if that was done in diversity, and there's no reason for bordering countries to feel somehow threatened by an expansion of influence of an enemy if it's your ally, and if his(/her/..) expansion of influence is your expansion of influence.
My initial argument was that the cause for the civil war isn't primarily Saudi Arabia, they came afterwards and i'm glad that this war has stopped before claiming even more victims.
However, i'd also like to point out that, without needing to really grasp the history of that country(, i'm obviously biased towards the leftists), there's a war because both sides haven't found a way to be united in diversity. And also that, e.g., the expansion of Iran wouldn't be a threat among allies, they always held an important part among muslims, Egypt and the Arabic Peninsula as well(, every muslim know that sunnis and shias can obviously live together). The so-called expansion of Iran in Yemen wouldn't mean much if its expansion already reached Morocco, and Saudi Arabia's influence already reached Indonesia ^(, there wouldn't be a point in saying "i'm closer to this country than you", such proximities would come and go without consequences). Who cares if our laws and our point of view aren't imposed in the countries we're united with, we'll learn from each other and lead with our example, at least we'll keep our own differences(, if our arguments ^(propaganda) beat theirs [1]), it's not that bad if they keep their own differences as well.
I.d.k., is it rational to claim that every single conflict would have been solved if both sides agreed to be united in diversity ?

[1] : If a strong enough group decides to establish a community inside a country, their will and number could force the government to allow them more diversity(, but sill in unity, with a common army, a set of common laws, some common medias, celebrations, languages, projects, enterprises, associations, and other ways to ensure a lasting friendship). There wouldn't be any territorial/economic/demographic/.. loss, separatism would be rendered impossible by the country, and forbidden by international laws, as would be not allowing most possible demands of differences.
The problem, however, could be that allowing the spreading of "othernesses" in our territory(, from inside or outside,) may result in the disparition of our own differences/peculiarities. Since i can't imagine the ideals of capitalism spreading like that ^(, at least not by the workers themselves), but only ideologies that i support, such spreading would represent the popular progression of ideas towards something better/'more just/virtuous/desirable/..', as long as it's natural.
As long as a (part of a )country agrees to be united, it should be allowed to become almost as different as it could ever want, even if it contaminates or is contaminated by the rest, as long as this contamination stays natural.
Capitalists-owned countries would refuse to unite with socialists countries because they're afraid of being unable to convince the ignorant workers that it's against their interests, it's always suspicious when a side doesn't feel confident enough to defend its position(, and in this case causes wars to avoid ever having to).

Since i'm already off-topic, i'd also add that the election of a law or president ^(for representative republics) should be canceled if the results promised/predicted aren't obtained.