According to irving janis (1972, 1982), groupthink occurs when groups value over
cohesiveness and solidarity;
a realistic consideration of the facts strong leadership;
weak leadership safety;
accuracy as many alternatives as possible; a common goal

Cohesiveness and Solidarity

Explanation:

The event that occurs when members of cohesive group are connected with quickly reaching consensus in their decision making without evaluating or critically analysing the ideas jis called groupthink. This term was given by William H. white and was studied by Irving Janis.

Janis analysed various foreign policy disasters such as Bay of Pigs invasion and Japanese attack on Pearl Harbour and found group cohesiveness to be the main cause for these. He found out that  cohesiveness of the group and Solidarity among the members to be main group properties for these attacks.