In the late 1990s and 2000s , international interventions authorized by the UN took a wider variety of forms . The UN mission in the Sierra Leone Civil War of 1991 – 2002 was supplemented by British Royal Marines , and the invasion of Afghanistan in 2001 was overseen by NATO.In 2003 , the United States invaded Iraq despite failing to pass a UN Security Council resolution for authorization , prompting a new round of questioning of the organization 's effectiveness . Under the eighth Secretary-General , Ban Ki-moon , the UN has intervened with peacekeepers in crises including the War in Darfur in Sudan and the Kivu conflict in the Democratic Republic of Congo and sent observers and chemical weapons inspectors to the Syrian Civil War . In 2013 , an internal review of UN actions in the final battles of the Sri Lankan Civil War in 2009 concluded that the organization had suffered " systemic failure " . One hundred and one UN personnel died in the 2010 Haiti earthquake , the worst loss of life in the organization 's history
the final battles
Alleged war crimes during the final stages of the Sri Lankan Civil War
United Nations