From the United States going outside the Security Council to launch the Iraq war to the spiraling violence in Syria and the nuclear march of Iran, it's been a tumultuous decade for the United Nations. Now, as diplomats head to New York for the annual General Assembly, we asked top experts and insiders to rate the U.N.'s biggest obstacles -- from hidebound bureaucrats to obstreperous member states -- and what role a body founded as the "last hope of mankind" should play on today's international stage. Is it outdated or simply indispensable?

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