With a Shi'ite rebel movement marching on Sana'a, Yemen, now seems like it's primed to be the next country in the region to stare down the prospect of violent collapse.

Yemen has always been one of the region's most problematic countries. Home to over 25 million people, it's one of the poorest countries in the Arab League and has one of the world's highest number of firearms per capita. It's home to Al Qaeda in the Arabian Peninsula, widely believed to be the jihadist organization's most dangerous franchise. The country is riven with complex regional, tribal, and sectarian dynamics that push back against any formal centralized authority — particularly in the three years since long-serving dictator Ali Abdullah Saleh was forced from power during the Arab Spring.