The regional strife in the Middle East, and America’s war on terror, is getting even more complicated as Saudi Arabia and its allies opened an air campaign to push back Yemen rebels. Ground troops are expected to follow. Here’s WaPo’s Ishaan Tharoor with an explanation of what the bombing of Yemen means for the Middle East.

+ Bloomberg: “Escalating chaos in Yemen threatens the Obama administration’s ability to combat the al-Qaeda affiliate that’s most intent on attacking the U.S. and its allies.”