Had another quick look...

IIRC from Duckweed's deity team game SG, an AI shouldn't be able to declare on a non-land-target if the target has more than 85% of its power. MM has actually had more power than Shaka all game, which should disqualify him. There's no evidence of significant military build-up, except for a small spike in the last few turns. Maybe he only went into war prep very recently, and needs some time. His WE is currently Posol (funnily enough, because he got hit for WE trade - love it when that happens). That's possible, I suppose, but I think we need to assume it's us.

Alexander actually also in WHEOOHRN. Have to think that Posol is a land target there. Maybe send a note to him, if we're hoping for long-term collaboration.