What is the role played by United Nations in maintaining world peace?
The Security Council is the UN organ which is responsible for resolutions on peace and security and for investigating possible threats to the world order. It is granted judiciary, legislative and executive powers by the UN Charter. The Council can take action for peacekeeping missions, military interventions and the infliction of economic sanctions to countries that are perceived as putting world peace and security at risk. The Council has 15 members, 5 of which (the U.S., Russia, China, the U. K. and France) are permanent and have the power to veto decisions while the remaining ten are elected every two years and haven't got any veto powers. To be effective resolutions must be approved by at least 9 members and do not receive a veto from one of the permanent members.
Much criticism has been levelled at the Security Council whose resolutions are often breached without consequences (see the massacres that took place in the former Yugoslavia in the 1990s or more recently in Darfur) or taken on account of the permanent members' economic interests (see the first Gulf War in 1991 following the invasion of oil-rich Kwait).