The United Nations was founded in 1945 in order to create a global collective security system for maintaining peace and security and saving the “succeeding generations from the scourge of war.” The structure of the organisation was a reflection of the world politics after the Second World War. Its Charter was based on the principle of national sovereignty, and its Security Council kept the privileged positions of the supreme powers by giving them permanent positions, and by providing them with a veto-right.

After the Cold War, the nature of conflicts started to change. The conflicts between nations decreased, giving space to new, internal conflicts. Today, conflicts within states are the most usual form of aggression and pose the greatest threat to international peace and security. However, a change of activity from across borders to activity within them has be-come a challenge for the international community and the United Nations.

The aim of this thesis is to show how the United Nations deals with international conflicts and to find out why the United Nations failed in preventing and stopping the conflicts in Rwanda, Bosnia and Kosova. In order to answer these questions, I have analyzed and pre-sented the Charter of United Nations and the actions taken by the Security Council during these three conflicts. These conflicts have been seen as the United Nations biggest failure by both the United Nations itself and the rest of the world. That is the main reason why these conflicts are part of my thesis. Moreover, all these conflicts are ethnic conflicts, where human rights have been abused and genocide has occurred.

The charter of the United Nations is based on the principle of sovereignty, which gives a state juridical supremacy within its own territory. Therefore, this principle together with the principle of non-intervention has limited the United Nations potential to act within states’ boundaries during ethnic conflicts. The collective security of the United Nations only func-tions when a clear act of aggression exists, veto is not applied and when the states with the military resources contribute in solving international conflicts. However, such a combina-tion seems rather impossible to be achieved within the United Nations, explaining why the genocide in Rwanda, Kosova and Bosnia could not be prevented nor stopped.