The Vietnam war which led to the loss of many American and Vietnamese lives because of extreme cohesiveness is an example of -

Group think

The correct answer is Option (3) → Group think

Group think is a psychological phenomenon that occurs when a highly cohesive group prioritizes harmony and consensus over critical evaluation of alternatives. In the case of the Vietnam War, U.S. policymakers continued with flawed strategies partly due to pressure to conform, suppression of dissent, and an illusion of unanimity, all hallmarks of group think. This led to poor decision-making despite evidence suggesting otherwise.