If you want to declair a war with another guild you must go to the Parilament Foreign Affairs building inside your guild fortress and find the guilds name in the list, once you highlight that guild you can select the War button and it will ask you for a confirmation, by clicking confirm you have sent the War invitation. (If a guild is still new it will give you a message saying you can not war this guild it is still too new).
That is all about it.
I am not shure how it is about accepting them but to semd the War Invitations.
That is about it
If you dont have the Parilament Foreign Affairs Building
You will have to build one of you want to make war with another guild
I said that if the guild was new you could not send War Invites
I also sugest you to not send them if your own guild is new
And dont accept them too.