Since wading into Yemen's civil war more than two years ago, Saudi Arabia and its allies have struggled to restore beleaguered President Abd Rabboh Mansour Hadi to power. Not only have Yemen's Houthi rebels proved to be determined adversaries, but the United Arab Emirates -- Saudi Arabia's most active partner in the military coalition -- has also steadily revealed strategic priorities in Yemen that often differ from Riyadh's own. Chief among them is Abu Dhabi's deepening crackdown on al-Islah, the Yemeni branch of the Muslim Brotherhood. And as the United Arab Emirates steps up its effort to take down the organization, it risks undermining any peace settlement its coalition allies support while empowering militant groups in the war-torn country....