Saudi Arabia went looking for allies against Ansar Allah, and so far it has gotten statements of support. Egypt has declared its readiness to back the Kingdom, but its statement does not commit to any military involvement. Pakistan and Turkey have pledged troops under the Mecca Joint Defense Agreement signed in August, but both governments say their forces will play “a supportive rather than active combat role” against the Houthis. I have watched coalition pledges like these for decades. Cairo...