How are Yemen's Houthis attacking Saudi Arabia so effectively?

LONDON — Houthi militants who control northwestern Yemen have in the past week attacked Riyadh international airport and hit the headquarters of Saudi Aramco, the world's largest oil company, in air assaults that have laid bare Saudi Arabia's vulnerability to threats from its enemy next door. The attacks are shattering the illusion of Saudi Arabia as a safe international investment hub as it tries to attract foreign money and diversify away from oil. This nightmare scenario for a key U.S. ally in the Gulf has been years in the making, weapons and regional experts say. They attribute Saudi Arabia's vulnerability to a ragtag group of Yemeni fighters to a perfect storm of factors that include Tehran helping the Houthis reach near self-sufficiency in producing and deploying advanced weapons, and the impact of the U.S. war on Iran that has depleted stocks of interceptors. Training to self-sufficiency by Iran Iran has been giving weapons, money and training to the Houthis, known formally as Ansar Allah, for more than a decade, although Tehran has officially denied arming the Houthis in violat