[quote=Toaw]
I have a question, if someone was to declare a war against the ruler of Lundland, whether it be for the throne, or just more territory, would the other players, since they are also vassals, have a noble obligation to protect, and defend him, and if so can we decline, and what happens if we do?
[/quote]

To help with your question, I'll talk about vassals first.

As a vassal of the realm, you are sworn to provide all the men you can muster to the aid of your liege lord in times of war, to uphold the claim of his legitimate heir to rule, and to not act with aggression toward him, or any of your fellow vassals. You are only allowed make war with another vassal unless a legitimate [i]de jure[/i] conflict occurs between you. Beyond that, you have no other responsibilities to your liege. Your liege's responsibilities to you are to protect you from unlawful aggression both foreign and within the realm, and to ensure your rights as a sovereign of the realm.

That's what's on paper, anyhow, but even those minimal responsibilities can become complex enough to provide an excuse for not accomplishing them. If your liege didn't protect you when a foreign threat came, he violated one of his duties to you, and you need not serve him until he answers this redress. If two heirs to the throne have equal claims to it, how can you be expected to uphold them both? If you have a document that claims your third cousin twice removed once happened to have promised to rescind control of a fief belonging to another vassal's House 50 years ago, would you be in the wrong for attempting to assert that claim?

To answer your questions; yes, but since your king has fallen into a depression so deep he can't even be assed to save his own skin, there will be little consequence to not helping him, [i]unless[/i] he recovers, manages to drive off the host that is currently laying waste to his land, and ask you to answer for your breach of feudal contract, or if someone else takes the throne and does the same.