The restive Yemeni northern province of Sa’dah, the power base of the Houthi rebellion, is close to the Saudi province of Najran, where a Zaydi minority and a majority of 1 million followers of the Shi‘i Ismaili sect reside. The rise of Houthi rebels along the porous Saudi–Yemeni border added an extra national security threat for Riyadh. Saudi authorities were confronted with serious security challenges along their 1,500-kilometer shared border with Yemen, including movements of terror cells and militant jihadists, smuggling of weapons and drugs, human trafficking, and the illegal entry of migrants.