There are three possible relations between Kings: Allied, Neutral or Enemy. All relations between Kings are Neutral on turn 1. All provinces not controlled by players are Enemies. At the end of any game turn, you may "Treat" or "Break Treaty" with other players.
When two nations are Enemies, they may attack each other freely. If two Kings have Neutral relations, their armies do not attack when ordered to move into the other King's province; instead, they remain where they are (this rule is especially useful when two countries plan to take the same non-player province in a turn). When two Kings are Allied, their forces and their Heroes' forces won't attack each other when in the same province and will try to add their strengths when in combat against a non-allied army. A province conquered by an Allied force belongs to the King with the larger army after the battle.
Some interesting cases arise when King X is allied to Kings Y and Z, who are Enemies. For example, either ally can march through the territory of King X to attack the other ally. Also, When King X leads forces present at the end of a phase in a province owned by King Y which has been invaded by King Z, his forces fight with King Y. Or, if Kings X and Z have Neutral relations, King X will fight with King Y. In none of these cases can King X ever assist in an attack.
A "Treat" order raises Enemy relations to Neutral, or Neutral relations to Allied, but only if both Kings "Treat" with each other on the same turn. The treaty lasts until broken.
When a Druidic kingdom Treats with another kingdom with which it has Neutral relations, the diplomats of the other kingdom will be swayed by the Druidic art of persuasion and doctrine of harmony. A treaty will be signed even without a reciprocal Treat order by the other King, unless the other King issues a Break Treaty order on the same game turn.
Druidics also ally more quickly. IF both a Druidic king and another king ally with each other, they become Allies before the turn begins, even if they were former enemies.
A "Break Treaty" order reduces the level of alliance one step (this gives an Ally a turn to reposition forces before war begins). When two Allies become Neutral and one player has some armies in the territory of the other, there is no combat. The armies may move to an adjacent Allied or Enemy province, otherwise they have little choice but to remain stranded where they are. If relations then become Enemy, there will be a battle unless one King moves his forces out of the province. If two Allies "Break Treaty" with each other on the same turn, they become Enemies.
An Evil or Undead King breaks a treaty at the beginning of a turn, not the end. Consequently, he may break a treaty with a Kingdom he has neutral relations with, and immediately invade it.
To exchange Sage discoveries, players need to have become Allies on a previous game turn. From then on, a mutual "Treat" order is interpreted as a scientific exchange. The only requirement is that at the end of the turn, the 2 Kingdoms are adjacent, or else a character from one Kingdom must be inside the other Kingdom. The two nations will exchange 1 secret for each mutual Treat order. Generally speaking, the secrets exchanged are the most military- oriented ones. The exchange takes place after finances are computed. The discoveries listed in your turn report will be shown in the order of their priority for scientific exchanges. If only one of the Kingdoms has a secret unknown to the other, one secret will still be given away.