How we change what others think, feel, believe and do
Groups will act to defend themselves, their beliefs and the things they believe they own. This is not only against external threat -- anyone inside the group who attacks it will be dealt with severely.
Groups, more or less, have physical territory. Companies have premises. Clubs use clubhouses. Gangs 'own' areas of towns and cities. These may be invaded, infiltrated or attacked by others who seek to gain entry or take over the territory.
The culture of the group, including core beliefs and values, is central to its identity. Attacking the culture may come from external criticism or the general influence of a large surrounding population. It may also appear where people within the group disagree with its leaders and ways. From minor irritation to outright revolution, internal threat can be particularly hazardous to the culture.
When an individual in the group is threatened in any way, whether physically or mentally, then the group will act to defend them. This is one of the basic tenets of tribalism: that, in return for compliance with group rules, you gain safety and protection. There is safety in numbers only if the group acts to protect each of its members.
Groups will both guard the boundaries and monitor internally. In companies there are security checks at the main entrance and reception with pass-card swipes for individual floors and departments. Clubs have membership cards.
Where there is an incursion from outside, there may be a practiced and regimented repulsion. There may also be a simple rushing to help repel the intruders.
A threat from within may well also receive a strong response, with transgressors being warned and then ostracized or ejected from the group.
Collaborative processes may be tacitly set up by which people never act in a way that threatens group harmony. National cultures can act this way too (for example Japan). This can become problematic, as in groupthink, where problems are studiously ignored even when everyone individually knows the group is on a self-destructive path.
Individuals may takes the role of 'guardian of the culture'. This is typically a leadership role, although individuals may also play this role. These 'mind guards' will typically have a 'friendly' word with those who transgress the written or unwritten rules of the group.
Other roles that may play a part in defending include border guards, judge, witness and participant in punitive measures.