How war will work

Starting a war:
When starting a war you should have a causus belli, which is fancy speak for a reason for war. Usually this will be the goal of annexing a certain area, or reconquest of an area that was taken from you before. Other ideas could be switching over control of specific puppets, releasing areas within peoples territories as puppets, etc, but keep in mind these can be complicated to put in place after a war is won/lost. When declaring your war, specifically state your causus belli. The causus belli should be reasonable:
An example of a reasonable causus belli is "Take Washington, Oregon, and Idaho from the Japanese." A reasonable causus belli is specific, not going to far, and generally nothing ridiculous.
An example of an unreasonable causus belli is "Destroy and annex Japan." This is unreasonable because it claims an entire country and eliminates them from the game, the claims are vague, such as the fact that Japan has puppets that could or could not be included in the war goal, and is generally ridiculous in its claim that it will destroy the entirety of a country.
When a war is won the only things that can be negotiated in a treaty are the original causus bellis. Therefore, if the Brits won a war against the Japanese with the causus belli of  "Take Washington, Oregon, and Idaho from the Japanese", the Brits could not annex California in the peace deal, only Washington, Oregon, and/or Idaho.  
When a war is started, the defender can at any time issue a counter causus belli, as long as it follows the guidelines for establishing causus belli. In the case of a defenders victory, these will be the items negotiated over in the peace deal rather than the attackers causus belli. In the case that the defender acquires a victory but fails to issue a causus belli, a white peace is signed and no changes are made.

Players in alliance with people at war must declare they are joining the war before fighting begins.

Fighting a war
Wars will be fought over a risk game. The game will start with each country having one troop in each territory that they control on the map of the world, as closely as can be reasonably achieved. Puppet countries armies will be under direct control of their owners unless the owner chooses to give ruler-ship of the puppets armies to somebody else. The rules will be as in standard Risk, except for the deployment of troops on the first turn. On the very first turn, players may choose between deploying by draft cards, or deploying by getting one troop for each province owned. This rule of deployment will only be used for the first turn of the game. If using a Risk Legacy board, no scars, faction bonuses, or otherwise non-standard rules will be in effect. Victory in Risk will be achieved in 3 ways: Capture of a players capital, total annihilation, or surrender. Surrender can be conditional, as discussed in negotiating peace. No players may join the war while fighting is happening, but as long as players declare they are joining the war before the dice roll to determine who goes first they may join the war. Allies cannot betray each other during fighting.

Negotiating peace
Only the causus belli can be negotiated over. The causus belli can be achieved in full, or only in parts. Victory by surrender can be conditional, and those conditions cannot be ignored in after-war negotiations. For example, if Japan surrenders to Britain, with the condition than only Washington will be annexed, in peace negotiations Britain may only annex Washington regardless of the original causus belli. Conditional surrenders may not include the surrender of anything outside the causus belli. In the case of victory by total annihilation or capture of an enemies capital, the victor is the decider of the negotiations.  Once the negotiations are over, the effects are put into place as soon as possible (message Tristan for map changes), unless the negotiations specify otherwise.
Other players in war negotiations
While peace negotiations are not required to be held in front of other players, they often will be. Anybody is allowed to interject into the conference and give points of view, but the decider of how the negotiations go is always decided by the victor. If players are dissatisfied with the results of a peace treaty, they are free to declare war as soon as negotiations end with a causus belli of "cancel the treaty of [x]."  However, all treaties must include a clause establishing at least 24 hours of peace between the two nations that were at war, so the loser will not be allowed to join a war to cancel the treaty unless it is declared after the peace period.

Note that these new rules are being tested and are subject to change, and may be entirely discarded if the concept doesn't work in practice.
Since NationStates gives us stats about our nations, we should put them to work. These rules focus on the population statistic that is available.

New mechanics
There are two new mechanics introduced in this revision: conscription levels and political power. Political power is used to increase conscription levels. Conscription levels go from 1 to 5, and affect how many people are recruited at the beginning of the turn. For the example, I will use my nation, Post Brexit Britain, as an example. At the time of writing PBUK has a population of 5 million. For each conscription level you get one soldier for every million population you have. So, at conscription level 1, the starting one, I would get 5 soldiers. At level 3, I would get 15 soldiers every turn, and at the highest, level 5, I would get 25 soldiers per turn.

Political Power
Political power is spent to increase conscription level. In the drafted version, it costs 50p to move from one to two, 100 for 2 to 3, 200 for 3 to 4, and 400 for 4 to 5. You start out getting 25 political power per turn, but this can be increased by using cards. Cards have been re purposed: they no longer give one time troop deployments. Instead, you can spend the resource points on cards to increase the amount of political power you get each turn. Currently this goes: 2 resource points for 25 to 40, 4 resource points for 40 to 50, and another 4 for 50 to 60.

Getting cards
Getting cards has been made easier to allow the game to flow faster. You will now get one card at the end of your turn if you:
-Take an empty territory
-Attack an enemy (you don't have to win)
-Choose to not recruit half of your soldiers (rounding down) for 1 card.

Update:
The player with the "largest army" stat starts all wars already at conscription 2