Siege mentality

Siege mentality is a shared feeling of victimization and defensiveness—a term derived from the actual experience of military defences of real sieges. It is a collective state of mind in which a group of people believe themselves constantly attacked, oppressed, or isolated in the face of the negative intentions of the rest of the world. Although a group phenomenon, the term describes both the emotions and thoughts of the group as a whole, and as individuals.
The result is a state of being overly fearful of surrounding peoples, and an intractably defensive attitude.
Characteristics.
Among the consequences of a siege mentality are black and white thinking, social conformity, and lack of trust, but also a preparedness for the worst and a strong sense of social cohesion.
Examples.
At a national level, siege mentalities existed in Soviet Union, Communist Albania, Rhodesia, Apartheid South Africa, and Northern Ireland during The Troubles, as a result of ideological isolation. The presence of siege mentality has also been described in countries such as North Korea, Russia, United States, West Bank, Israel, Taiwan, Venezuela and Poland, where it is arguably encouraged by both the government—to help justify their continuance in power—and the opposition—to help justify their overthrowing the government through violent means.
In Poland, the LGBT ideology-free zone could be likened to the siege mentality, in which the government treats LGBT people as a danger to the country. Some of Poland's most prominent conservative politicians, including its president, Andrzej Duda, have spoken out about the purported dangers of the "LGBT ideology". This creates a suspended state of fear and resentment in line with the definition of a siege mentality. 
Sociologically, the term may refer to persecution feelings by anyone in a group that views itself as a threatened minority, as with the early psychoanalysts. This can be used for example in the field of sports, where coaches or managers often create a siege mentality in their players by highlighting an environment of hostility from outside the club (whether the hostility is real or exaggerated is irrelevant).
Siege mentalities are particularly common in business, the result of competition or downsizing, though here the (smaller-scale) alternative of "bunker mentality" (analogous to soldiers who have taken shelter in a bunker) may be used. Some religious groups may have this paradigm, particularly if they are not traditional mainstream groups.
Literary analogies.
Seamus Heaney used the phrase "Besieged within the siege" to describe the feeling of the beleaguered Catholic minority in Northern Ireland within the broader siege mentality of the Protestant community itself.
See also.
Related psychological behaviours: