How does this sound

No consent needed, however wars must be declared
To declare a war the declaring nation should make a forum post and PM the nation he/she is declaring war on (the PM is just in case the nation war is being declared on doesn't see the post)
To actually have troops you need to have filled out and posted a link to the regional military spreadsheet. Said spreadsheet can be downloaded here: http://novahistoriae.smfnew2.com/index.php?action=ezportal;sa=page;p=1
Wars will be turn based. In other words the first person to post should only post a single action declaring units they are moving/using and their actions, the next person to respond will declare any defensive actions taken then units they are moving/using and their action, and so on until all nations involved have posted.
Nations who are being attacked will have 48 hours to respond to a post/attack. If they do not respond within that time frame it will be assumed that they were unable to defend against that particular attack and the territory/city in question was lost.