Why can't I suggest war against Japan or a specific civilization?

I'm playing a (built-in) custom map and Japan is attacking everyone, even the kittens! They've attacked one country I'm on excellent terms with but the game lets me suggest going to war with ONLY everyone except Oda from Japan. What the heck is going on?

Solution 1:

A few possibilities:

• Is the nation you're talking to already at war with Japan?

If so, you can't suggest a mutual war-dec, although you should still be able to offer to war-dec Japan as part of a trade (but not request it from your trading partner).

• Are you already at war with Japan?

If so, you can't suggest a mutual war-dec, although you should still be able to request that a trading partner war-dec Japan in return for something you trade (but not offer it yourself).

• Has the other nation been at war with Japan in the last 10 turns?

When a peace treaty is signed the nations involved in them can not go to war again until 10 turns have passed.

Remember than when Japan attacks another nation, not only does Japan go to war with that nation, but that nation also goes to war with Japan. If they've already been attacked or are attacking Japan, then they're already at war, and you can't suggest they do something that they're already doing.