In Tribal Leadership: Leveraging Natural Groups to Build a Thriving Organization, authors David C. Logan and John King draw from several decades of consulting experience to examine the corporate cultures at a number of leading companies, including Amgen, Intel, American Express, and Prudential. What makes these companies so successful? Tribes - the groups that naturally form within the company - are the secret to lasting success, the authors say. Birds flock, fish school, and people "tribe.