The United Nations was created in 1945 to replace the failed League of Nations and work to prevent world wars. It aims to maintain international peace and security through efforts like peacekeeping operations. The UN has had some successes in ending conflicts but has also faced challenges and failures that have provided important lessons. Key factors for successful peacekeeping include support from member states and parties to conflicts, as well as upholding principles of consent, impartiality and only using force for defense.