Group dynamics are complicated and can make or break a team.
This is why effective communication is vital to a team's health. Encourage the group to discuss issues or conflict among themselves as they arise. If a conflict is left hanging and isn't addressed, it quickly becomes like a cancerous growth, spreading negativity among the group members. Sure enough, the involved parties will talk to other group members about the situation and, before you know it, team members will have chosen sides based on loyalties. The team is no longer united as one, but instead has been split into smaller teams that are now pitted against one another.