Yemen is the latest country in the region to collapse. Shi'ite rebels have taken control of much of the country and Saudi Arabia has launched a military campaign to re-install the ousted government. It's a complex mess, with regional rivalries and local grievances overlaid with sectarian strife. ISIS and al Qaeda are getting in the game, too. If present trends continue the situation could reach Syrian levels of depravity. 
On the line today to discuss the underlying causes of the conflict, help understand the exact nature of Iran's role in this crisis, and recommend ways that Yemen can avoid a death spiral is April Longley Alley of the International Crisis Group. If you have 15 minutes and want a textured understanding of what's happening in Yemen--and why--have a listen.