When you declare war, you can see if allies are willing to join. If not, you can hover "no" and see why. In the case of a league its members always defend each other no matter what while your Argos, of course, wouldn't want to go to war with additional enemies who are stronger than it. Especially if it's already war weary or has few money. It reminds me of Vicky 3 where I like the diplomatic game system and that you can entice others to join if you have something they want. Would be nice to have here something like that too,

Originally posted by Menkerot:

When you declare war, you can see if allies are willing to join. If not, you can hover "no" and see why. In the case of a league its members always defend each other no matter what while your Argos, of course, wouldn't want to go to war with additional enemies who are stronger than it. Especially if it's already war weary or has few money. It reminds me of Vicky 3 where I like the diplomatic game system and that you can entice others to join if you have something they want. Would be nice to have here something like that too,

You mean it is bugged?

Now Megalopolis allied with argos and is in war with one of the city states in the league. But Megalopolis is still also in the league lol.

This game is so broken it is unplayable.

It's not broken. It's in war but not with the whole league because Argos called it and since Argos is fighting only one state, its ally too. Most of the time it doesn't matter tho because Greece is gobbled up by Thrace / Antigonids / Macedon and later Rome anyway.

If Argos is at war and doesn't call you, declaring war against the same enemy will create a new war with another goal. You cannot merge two wars. So no, Argos won't join, even after finishing its war as it'll provoke a truce break on their side, which decreases stability.
No bug here.

Plenty of factors can explain why Argos isn't at war with the whole league (like declaring war on an enemy that isn't in the league but has an ally that is in the league, and Megalopolis can join this war despite fighting a member of its league, just because the defender isn't in the league).