What happened in the “Robber’s Cave” experiment? Why is that study significant?

The Robber's Cave experiment was conducted in 1954 by a famous social psychologist, Muzafer Sherif. In this experiment, 22 12-year-old boys from white, middle-class, Protestant backgrounds with two parents were brought to Robber's Cave State Park in Oklahoma. They did not know each other before the study and were randomly assigned to one of two groups. Each group spent a week developing their own group norms without being aware of the other group. One group called itself the Rattlers, while the other group called itself the Eagles. During the competition part of the experiment, the boys engaged in competitions that led to all-or-nothing awards (the winners got everything, while the losers got nothing). For example, picnics were staged in which the first group to arrive ate all the food. The conflict between the groups started as verbal harassment and developed into stealing each other's property and then physical attacks. During the last two days of the experiment, the boys spoke in a debriefing exercise of the negative qualities of the other group and the positive qualities of their group. The conflict between the groups was lessened through inter-group activities that involved teamwork. 
The experiment is important because it corroborates Sherif's Realistic Conflict Theory, which states that conflicts between groups are an outgrowth of limited resources and situations in which only one group can achieve rewards. This type of conflict results in the members of one group developing negative stereotypes about the other group, even if the individuals in one group are quite similar to the individuals in the other group.