Rough draft of the War Aims system I'm going to use (adapated from SoM)
War Aims are CBs that reflect what you're aiming for. When going for peace, you can demand more or less than what your war aim was but there will be penalties in either direction. Less and your people will be angry for five years resulting in a -3% domestic income for each year they're angry. However, claiming more opens a CB on you (Belligerence). Getting this "just right" means +2% domestic income for five years.
When you go to war, you can set your war aims and as many as you want. If the war continues for three years, you're allowed to add MORE to your aims but not take back any previous aims. Nations on the defense can't have any war aims except to demand Reparations at the outbreak of the war. However, if the war lasts three years, the defender can add war aims.
The following are some of the war aims.
-Embargo or Blockade: This war aim demands you break their blockade and/or embargo on you..
-Belligerence; if the enemy waged a war without a casus belli, you get one against them. This one is a freebie. Feel free to do as much or as little damage as you want and get off scott-free for a white peace. You can't keep territory. But you can demand reparations and arms reduction and many other things.
-Balance of Power: When a single nation is 100% more powerful than any nation on the planet, you can declare war on them. To achieve this aim, you must settle on a peace treaty that brings them on par with the next leading nation.
-Overlapping Claims; if you both claimed the same province and can't work out a peaceful resolution, you can try and take it by force of arms. War aim is simple.
-War of Liberation; you can attack your opponent if they've recently vassalised or annexed a state by force. Achieve this aim simply be getting the vassal/annexed states released. You can also use this to liberate colonies, creating an independent nation.
-Guarantee of Independence; if your enemy attacks someone who you've guaranteed, or who is your ally or vassal, you have permission to strike them down to protect your honor. To achieve this aim, demand reparations for your ally or vassal or gurantee-ee.
-Colonial War: Declare war on someone to take one of their colonies.
-Loan Collection: If a nation defaults on their loan, the nations who had loaned money to that nation gain a CB on them. To achieve this aim, declare war on them and demand the money owned.
-Cancel Trade Agreement: If a nation doesn't want to cancel the trade agreement with your nation, you can declare war on them and force them to cancel it.
-Dishonored Alliance: If an alliance is dishonored, the signatories of the alliance have the right to declare war on the one who dishonored the alliance. Achieve this aim by demanding reparations.
-Annexation: Only avaible against nations tech five levels under yours. You can go in and simply annex them.
-Puppet: Only available against nations with tech three levels under yours. You can go in and carve out a puppet state.
Any more ideas?