Diplomacy Rules Summary

I want to do this thing methodically, so the logical place to start would seem to me to be the game rules. So in this post I will go over the rules of Diplomacy in my own words. I'll follow it up soon with a post covering the basic types of negotiations that occur in a typical game.

The Board

The Diplomacy board consists of a map of Europe and the northern tip of Africa. Both the land masses and water bodies are divided by borders into a number of regions - topographically this shape is described as a planar map. The regional division is done in such a way that no two borders cross completely over each other - at any intersection one of the borders always stops. In other words there are no regions in the map that are diagonally adjacent (touching only at a point). All adjacent regions share a boundary of non-zero length.

Some of the land regions contain circular icons known as supply centres. They indicate that the region has strategic significance within the game. There are 34 supply centers on the board, and a player wins Diplomacy when they control more that half of the supply centers on the map.

The sea and ocean regions are usually much bigger than their land counterparts, with each water region bordering several land regions along its coast(s). This causes the in-game effect that sea travel is faster than land travel in the game - as it is in reality.

The regions of Kiel and Constantinople have channels that allow traversal by fleets without having to follow the coast. Several regions, including Iceland and Switzerland, are considered impassible in the game. No unit can enter these regions, and they can prevent regions on either side from being adjacent.

The Units

The units in Diplomacy represent the armed forces of your nation. Units are placed within a region of the board, and each region may only contain a single unit at any point in time. All pieces have equal value - the only differentiation between pieces is their unit type; they can be either a fleet or an army. This means that the only way to concentrate your forces is to occupy a large set of adjacent regions, which favours a sound strategy over the brute force approach.

Movement is allowed from the unit's current location to an adjacent region (one that shares a border). Of course no unit may ever move into an impassible region. Armies may never move into a water region but are otherwise unrestricted.  

Fleets may move freely in water regions, but are restricted on land to coastal regions - those bordering a water region. Furthermore when moving from one land region to an adjacent one, fleets must follow the coastline - they cannot move across the land to another coast. The exception to this is when a channel is present, as mentioned above.

Gameplay

The game starts in the year 1900 with each player being allocated to one of the seven nations: England, France, Germany, Italy, Austria, Russia and Turkey. Each nation starts with three supply centers under their control, and each supply center region contains a single unit of a specific type. Except Russia, who for some reason starts with four supply centers and units - lucky Russia :)

Gameplay is divided into a number of years, which is further broken down into three seasons: Spring, Autumn and Winter. Year follows year until one player becomes the overall winner, or until everyone gets tired and goes home... Diplomacy can go on for a long time, and in some scenarios it is even possible to reach a stalemate.

The Spring and Autumn seasons both consist of players choosing an order of each of their units and then resolving everyones orders simultaneously. These two seasons are identical rules-wise. After conflicts are resolved (see below) a separate retreats phase may be required.

The Winter season in when all the nations rest up and consolidate the new lands they have captured. During this phase any supply center region containing a unit falls under the control of the unit's controlling nation (if it wasn't already). Then the number of units controlled by each player is adjusted so that it equals the number of supply centers controlled by that player. Lucky players get to build new units of either type. Those less lucky must choose which unit(s) to destroy.

Players can only build new units within the initial supply centre regions they began the game with. This of course means that these regions must be vacant in order for new units to be build. In practice this is usually the case as units move away from their starting locations and towards the front(s). The second build restriction is common sense - you can only build fleets on coastal regions!

Conflict

There is just one more thing for me to explain and you have learnt all the rules to the game; and that is what happens when two units try to move into the same region. The method of resolving conflict in Diplomacy is conceptually simple and straightforward - but it can become confusing when larger groups of units are involved in a combat, and they are all jostling with each other for position.

Conflict occurs in two scenarios: when a unit tries to move into an already occupied region; and when two units try to move into the same region. The basic tenet of Diplomacy conflict resolution is that all units are equal, and that you need to have more force that your opponent in order to move into a region. In order to do this you need to issue support orders.

Support orders are orders given during Spring or Autumn in lieu of movement. There are two types of these orders - support move and support hold. Support orders allow multiple units to combine their strength in order to overwhelm opposing forces - or to resist such attacks. A support order is cancelled if any unit attempts to move into the region occupied by the supporting unit - the support order is immediately changed to hold. This does not apply if the attacking unit is coming directly from the region being supported.

A support move order indicates that the unit specified is going to support another unit in its movement to a specific region. The supporting unit must be legally able to move into the region that it is supporting movement into. This means that the region must be adjacent, and fulfill the movement restrictions of the unit's type.

A support hold order allows a unit to help an adjacent unit resist a supported move. Like a support move, the supporting unit must be legally able to move into the region of the holding unit it is supporting. 

To determine if the move is successful, the number of units supporting the move must be greater than the number of units supporting the hold. When this occurs, the original occupant of the region must retreat to an adjacent region with a legal move. If this is not possible then the unit is destroyed.