If a group of people have a siege mentality, they think that other people are constantly trying to harm or defeat them, and so they care only about protecting themselves.
Police officers had a siege mentality that isolated them from the people they served.
siege mentality in British English
noun
a state of mind in which a person believes that he or she is being constantly oppressed or attacked
siege mentality in American English
an attitude or state of mind in which one feels surrounded or under attack by enemies, opposition, etc.
Examples of 'siege mentality' in a sentence
siege mentality
We have to guard against the siege mentality.
Christianity Today (2000)
The siege mentality has brought a togetherness that would have been unimaginable a matter of months ago.
Times, Sunday Times (2011)
Once again he has built a siege mentality at his club.
The Sun (2011)
It was childish and showed a needless siege mentality.
The Sun (2016)
There must be a siege mentality.
The Sun (2013)
It might foster a siege mentality.
Times, Sunday Times (2014)
The lack of coverage of her success fuelled her siege mentality, and she grew confrontational in interviews.
Times, Sunday Times (2013)
Sometimes we bunker down, adopting a siege mentality, whereas we should be proud of working hard.