A stab (short for backstab) is when a power breaks an agreement with another power. Stabs are one of the most recognizable and most dangerous strategies in Diplomacy. A stab involves betraying an ally for the chance to increase one's own strength. Indeed, the stab is more art than strategy. In order for the stab to be successful, the target must not suspect anything or, save that, be unable to mount an effective defense in time. The stab is by far the riskiest move a player can make. While the rewards can be big, a betrayed ally can become a powerful enemy. In addition, if one stabs too often, he or she may find it difficult to find allies in the current or future games.
Types of stabs
There are several types of stabs, some of which are listed below.
Enter a territory which was previously agreed upon as demilitarized zone
This is one of the least aggressive stabs, and will sometimes be forgiven directly afterwards, especially if the stabber aids the victim in some other way. It is often a preparation for an attack though.
Failing to support an ally's attack
This is often a subtle stab, but may not gain much. The chance of the stabbed player turning directly on the stabber is reduced, especially in the early game, since the stabbed player is already involved in a war (hence his original attack, which the stabber failed to support).
Failing to support an ally's defence
This kind of stab is often on the same scale as attacking the ally, especially if the failure to support leads to the ally having to retreat.
Attacking an ally
Attacking an ally will almost always lead to war.
Enter an ally's supply centre
This is probably the most profitable type of stab. Always beware of it, and look out for opportunities to do it.
Normally the stabber plans to take more than just one supply centre from their ex-ally. The stabber has to make sure the stab-ee cannot recover in anything close to a timely fashion. The key point is that you gain centres at the same time your opponent is forced to disband units. If both you and your ally have six units each when you take the opportunity to stab them in the Fall, you want to make sure that you can steal at least two of his centres. If you do, the balance of power shifts from parity to eight vs four. It doesn't much matter how angry the stab-ee now is, they are half your size and (all other things being equal) will not last much longer in the game.
Opponents don't forgive this type of stab easily, so be very aware that once you have guided your dagger between the ribs, it is no time to stop attacking or to think about patching things up. You are best advised to rain blow after blow on your opponent until they are totally broken.
The Strategic Stab
This is where you take a key centre of strategic importance off your ally. A good example is when England steals St Petersburg from Russia. England is a naval power and removing Russia's ability to build any more fleets in the North is of great worth to England..
How to react when you get stabbed
It can hurt. You feel betrayed. (You HAVE been betrayed!). You want revenge. If your ally has stabbed you at the right time you may be too weak to take him on. Your best approach is to send a message to the person that stabbed you, something like "Ouch! That really hurt! An impressive stab - you got me there! But I see that our neighbours are looking threatening. I am happy to forgive and forget. Let's deal with the REAL enemy"
If you CAN get back on good terms, you can survive and grow - then you can time your counter-stab when it does the most harm.
Stabbing and secret alliances
Alliances which are kept secret and intended as a surprise, are especially susceptible to stabs since the only player who will know of the stab is the stabbed player, and the player's reputation might remain intact. It is not uncommon for players to make alliances or non-aggression pacts with all their neighbors during the first spring, and when they have no more neutrals to expand into whichever of their alliances is most opportune.