Although structures are highly important because they provide the context for what is possible and what is not, without actual people nothing is done. Thus, in business or diplomatic negotiations, personal relationships between key stakeholders are often crucial. This chapter demonstrates that when new subregional multinational defence cooperations (MDC) have been established, key stakeholders from at least two defence policy communities (DPCs) worked closely together and took leadership to initiate new cooperation. The most important precondition for this was that these stakeholders had to like each other. This insight corresponds with the practical experiences of diplomats, who observe that when people in critical positions from different countries like each other and establish a good working relationship, significant progress can be made in a very short period of time on issues that had been stalled for years (Witness Seminar, 2019). They also notice that progress can still be made without interpersonal chemistry between leaders, and especially when frameworks or institutions are already in place, gradual improvements can be made too. These institutions can even serve to maintain healthy relations between countries at the technical level when the relationship between the leaders deteriorates significantly. However, good chemistry between leaders almost always boosts cooperation. This chapter thus describes a situational factor that can be described as ‘Strong leadership by a group of enthusiastic highlevel officials and good interpersonal chemistry between them’. It points out that structural factors are not enough to launch new MDCs and explains how interpersonal chemistry among the key leaders plays a crucial role in establishing new defence collaborations. This chapter applies the insights of social psychology, focusing on the research regarding interpersonal attraction.

Interpersonal attraction has an extensive literature in psychology that studies why certain people like and are attracted to each other and why others not (Huston, 1974; Hogg and Turner, 1985; Klohnen and Luo, 2003; Montoya et al, 2008; Finkel et al, 2015). People can find others attractive for different reasons, and attraction can lead, for instance, to friendships, romanticrelationships or good business partnerships. The underlying dynamics of attraction in each of these social settings are very similar, and empirical research shows that the most relevant variables for developing interpersonal attraction are propinquity, similarity and physical attraction.