A rebel group from the North of Yemen has taken over the capital and drastically changed Yemen's political landscape. Engaged in a proxy war between Iran and Saudi Arabia, the Houthis have brought Yemen to the brink of collapse. But who are Yemen's Houthis? What do they want? How have they come to take control of huge parts of the country? Safa Al-Ahmad from BBC Arabic has spent 3 months following the Houthis and also gets extraordinary access to their arch-enemies, the Sunni tribal leaders and other fighters loyal to Al-Qaeda.