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 defense
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 center
This is probably the most profitable type of stab. Always beware of it, and look out for opportunities of it. Normally the stabber takes more than just one supply center from his ex-ally. He has to make sure the stab-ee cannot recover in anything close to a timely fashion. Ideally, about 5-6 centers are taken in the Fall turn.
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.