To understand the occurrence of reciprocation, we must consider the ways in which the prior actions of another nation may affect decision makers' expectancies and the values they give to various possible outcomes of the interaction. Cooperative prior action by the other tends to raise the actor's expectancy that his own cooperative action will result in mutual cooperation and also to increase the intrinsic value of cooperation. Conflictive actions by the other nation will tend to raise the value that decision makers place on winning over the other and to decrease their expectancies that cooperative behavior will result in mutual cooperation. While the prior actions of the other tend to lead to reciprocation, its occurrence depends also on other factors that affect national leaders' expectancies and values. Relevant other factors include the extent to which the nations are dependent on exchange relations with each other and the relative power of the two sides. Mutual reciprocity is most likely when there is a high and balanced level of exchange and when the power of the two sides is about equal.