The first factor are pre-existing bonds. When groups did not know each other yet, they often held stereotypical ideas about each other, which –at least initially- stopped them from joining. Knowing each other however was not always conducive for cooperation either. Often previous attempts to cooperate had failed, leaving people with negative experiences, reducing the willingness to cooperate again.
The second factor I identify is identification, i.e. the perception to which network one belongs, regardless of whether one actually knows people in that group or not. Organizers who identified with universalistic groups, such as the alterglobalist movement, were willing to cooperate with others (whom they all saw as part of ‘us’) and they were motivated to include ever more groups in the cooperation and tried to keep everyone involved, even when cooperation was difficult. On the other hand, organizers who identified with particularistic groups, joined the cooperation to strengthen their own particular group and reach their own group’s objectives. They were therefore less inclined to join, to listen to others, or to stay when cooperation got difficult.