The United Nations came into being in 1945, following the devastation of the Second World War, with one central mission: the maintenance of international peace and security. The UN does this by working to prevent conflict; helping parties in conflict make peace; peacekeeping; and creating the conditions to allow peace to hold and flourish. These activities often overlap and should reinforce one another, to be effective. The UN Security Council has the primary responsibility for international peace and security. The General Assembly and the Secretary-General play major, important, and complementary roles, along with other UN offices and bodies.

One of the purposes of the United Nations, as stated in its Charter, is "to achieve international co-operation in solving international problems of an economic, social, cultural, or humanitarian character."  The UN first did this in the aftermath of the Second World War on the devastated continent of Europe, which it helped to rebuild.  The Organization is now relied upon by the international community to coordinate humanitarian relief operations due to natural and man-made disasters in areas beyond the relief capacity of national authorities alone.

The UN Charter, in its Preamble, set an objective: "to establish conditions under which justice and respect for the obligations arising from treaties and other sources of international law can be maintained."  Ever since, the development of, and respect for international law has been a key part of the work of the Organization.  This work is carried out in many ways - by courts, tribunals, multilateral treaties - and by the Security Council, which can approve peacekeeping missions, impose sanctions, or authorize the use of force when there is a threat to international peace and security, if it deems this necessary.  These powers are given to it by the UN Charter, which is considered an international treaty.  As such, it is an instrument of international law, and UN Member States are bound by it.  The UN Charter codifies the major principles of international relations, from sovereign equality of States to the prohibition of the use of force in international relations.