One of the design pillars of upcoming grand strategy game Victoria 3 is for diplomacy to be just as powerful a tool as warfare is - the latter is, after all, the continuation of the former by other means, as Carl von Clausewitz is often quoted as saying. Victoria 3's diplomacy system is almost a game in itself, giving you plenty of options for winning an exchange with another nation without ever having to fire a shot.
The latest Victoria 3 dev diary goes deep into 'diplomatic plays.' These are the opening moves for any conflict in Victoria 3, so you'll inevitably go through the process prior to any war. Diplomatic plays begin with opening moves that correspond to the war goals you may be familiar with from other Paradox games: you'll make a play to annex another nation as subject, or to demand that it cede territory to you, or to abolish slavery.
Once you've picked out your play, the target will be notified, along with any nations that have a strong interest in the region and are considered 'potential participants' in any resulting conflict. Overlords and allies, for example, are going to take interest in what happens during negotiations.
RELATED LINKS:
In Victoria 3, your admirals are the key to dominating the sea
Victoria 3 will make war a truly industrial affair
Warfare in Victoria 3 will be a radical departure from other grand strategy games