the sunni/shia thing is a tool to promote various conflicts, rather than the point of the conflict itself. well, there may be some legit nutbars in saudi arabia. but it's a secondary concern. it's not hard to guess what it's actually about. it starts with an 'o' and rhymes with "coil".
take a step back. the meta conflict remains the cold war. the intelligentsia has wanted to move on for years, but it's a lot of delusional neo-liberalism. history didn't end. it didn't even shift. same shit carried on without a blip. it's just that the americans got a step up on the game. what's been happening since 1990 is that russian influence has been waning, and the chinese haven't been able or willing to step in, which created a power vacuum. the various proxy wars are the result of local interests stepping into this power vacuum and jockeying for control.
so, you've got this saudi arabia v iran thing. but this is not the dominant conflict. the saudis are armed to their teeth with billions of dollars of us arms. the iranians know better than to poke them. it's a conflict that's over before it starts. even the israeli intelligence people have come out and stated that iran is unable to pose any kind of a military threat to anybody in the region.
rather, the dominant proxy war happening right now is between turkey and saudi arabia. unlike the iranians, the turks are serious players and pose a serious threat to saudi ambitions in the region. europe's continual refusal to allow turkey in (and if i were turkey, i wouldn't even want in at this point) has forced them to focus to their south. syria. iraq. egypt. all this instability is the result of turkish aligned groups fighting with saudi-aligned groups to walk into the vacuum created by the assumed inevitable russian pullout (which is in fact not inevitable, and not happening).
meanwhile, america is doing what the british have been doing for centuries, which is keeping everybody at each other's throats and profiting off the conflict from all sides.
i mean, what's been driving this mess in syria is the question of which american ally is going to take over when the russian-backed assad regime falls - the saudis or the turks. but, in fact, it seems as though the russians are going to maintain control of the region, even if it means that all that's left of it is a pile of rubble.
and the saudis and turks are reduced to bickering amongst themselves on the iraq/syria border, while the kurds are all like "hey, wait a minute here..." and the population is increasingly siding with iran as a stabilizing force.