Question - Knight Commander

Good evening/morning/afternoon all (depending where in the world you're reading this right now). Quick question for those who enjoy a spot of Knight Commander
when they have a bit of time to kill: how is one supposed to go to war? I've scoured the userguide several times, and other than telling me I can go to
war by going into the shop screen it provides no other useful instructions regarding how to go about it. Actually when I scour the shop screen there's
nothing in there giving me a go to war option. Many thanks in advance for any help.