The experiment of the Cave of the Thieves is one of the classic researches of Social Psychology. Made in 1954 with 11-year-old teenagers, it was conducted by University of Oklahoma professors Muzafer and Carolyn Sherif in an attempt to understand the origin of prejudice in social groups. Known as Robber's Cave State Park, in the state of Oklahoma, Sherif was introduced in the study to the 22 male teenagers who would take part in the experiment as the camp manager. The teenagers were transferred to the camp in two groups, each consisting of 11 boys. One group was unaware of the other and since they were assigned to two different and distant areas, they did not even meet during the first few days. Later each group chose a name that identified it: “The Eagles” and “The Rattlers”. But… what were the hypotheses that motivated the experimenters?1. If people have not established any kind of relationship with each other, will they show a tendency to work together and set common goals and will a group structure develop?2. If two groups were formed under conditions of group competitiveness and frustration, will they develop hostile attitudes in relation to the members of the other group?The 22 adolescents came from the middle class of Protestant religion, had presented a normal psychological development and appeared to be boys who practiced the social rules of behavior. The participants did not know each other before, in order to avoid the existence of small sub-groups prior to the experience. The experimenters promote the common goals for which a cooperative discussion was needed, the planning of activities and the consequent implementation of the same. By the end of the first five or six days, their respective social hierarchies had already developed within each group, and the boys recognized themselves as an integral part of the group. their sense of belonging to their own group and establish barriers between their own and the other group. Researchers were usually asked to organize competitions with the opposing group. In this way, the effectiveness of the group increased to the same extent that the hatred for the other group increased. The boys felt pressured to unite to fight an apparent external enemy, at which point the researchers smoothed out conflict between the two groups through competitions. It was said that they would give a trophy to the winning group, and at each competition they would accumulate points that would bring them closer to winning the trophy. At the same time, individual trophies (objects that children of that age particularly desired) were awarded to those participants who would have distinguished themselves for their performance. From this moment on, attitudes of antipathy began to show themselves in an evident way; the boys of one group did not want to eat with those of the other, showed themselves disrespectful towards the flag of the opposite group and made vulgar allusions to the opposite group in a very irreverent way. experiment, in which the aim was to eliminate these feelings that generated aversion and competitiveness in order to integrate both groups. However, the activities planned together, such as watching movies or throwing fireworks on the 4th of July, had no effect, on the contrary, at the end of these activities there were clashes between the members of the two groups. activities that had goals that transcended a particular group; for example “the water problem”. This problem confronted the boys with a fictitious situation. One day the water supplies ran out and the researchers blamed some "vandals in the area". Both groups began the search for water until they encountered a tank which needed to be fitted with a tap. Evidently, joint work by the two groups was needed to achieve the goal, and so it was done. The excitement was so great when they saw the water come out that the members of the first group had no objection when the boys of the second group drank first.Another problem was the presentation of a film that was in vogue at this time. for kids their age. Almost everyone agreed that they wanted to see the same movie, then, the researchers told them that the screening cost $ 15. An amount of money that neither group could ever have raised separately. At this point, all 22 boys pooled their savings to get the amount needed to see the film all together. After various tasks of this kind, the members of each group joined in common activities and gave up their competitive spirit. The success was such that even when it came to going home, they asked all together to get on the same bus and when they stopped for a rest break, the members of the "Ratters" group paid everyone a drink with the money they had. These results were obviously very interesting, perhaps a little worrying for those who are used to always seeing life in a negative perspective, but they inspire some hope. In fact, we see how people, as long as they have common goals, can stop having prejudices and are willing to work together by breaking down barriers. In any case, I would like to emphasize the effect of the "common enemy", a phenomenon that has a long history and which has served the purpose of manipulating the masses over time. We all know that, regardless of all the positive effects that the fact of belonging to a group may have; the groups, during the process of building their identity, do nothing but outline barriers between themselves and others, sometimes these barriers are more flexible, other times more rigid and discriminating. It is a classic principle on which the great manipulators of the masses of the past and present such as Hitler and the various political pseudoleaders of yesterday and today have been based: creating a common enemy to foment the sense of belonging of people to a group.