The UN calls Yemen 'the world's worst humanitarian crisis'. It says more than three-fourths of the population - over 22 million people - are in need of humanitarian assistance. Yemenis face hunger, disease, and the terror of a war which has pitted Iran-backed Houthi rebels against a military coalition led by Saudi Arabia. This week marks the end of the third year of that Saudi campaign - with no end in sight. Yemen's Minister of State resigned Wednesday saying Yemen's President, Abdrabbuh Mansour Hadi was under house arrest in the Saudi capital, Riyadh. So what are the Saudi aims in Yemen and why are Yemeni civilians continuing to suffer so much? Carrie Gracie and a panel of expert guests bring clarity to one of the world's most complex wars.