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

LONDON – Houthi militants who control northwestern Yemen have in the past week attacked Riyadh’s 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.