The United Nations' founders set out 70 years ago to prevent another world war. In that, they succeeded to date, but there has been no shortage of crises and conflicts to test the organization.
The world body has grown over those years and as it moves into its next decade will decide what it needs to do to stay relevant going forward.
The United Nations was born out of the ashes of World War II and the failures of its predecessor, the League of Nations.
At a conference in San Francisco in 1945, the organization’s charter was drawn up, seeking to foster a more peaceful world and promote and develop human rights.
President Harry Truman told delegates there were many who doubted they could succeed because of their differences.
“But these differences were all forgotten in one unshakable unity of determination - to find a way to end war," said Truman.
That October, the United Nations was officially established after 29 of its first 50 member states ratified the charter. Today, there are 193 member states.
Michael Doyle, an advisor to former Secretary-General Kofi Annan, says the organization got off to a rocky start.
“During the Cold War, the split between the Soviet Union and the U.S. created an institution that was at loggerheads with itself. It could only work in the margins in peacekeeping, and those particular conflicts where the U.S. and Soviets wanted to take it off their own rivalry and let it work on the side," said Doyle.
U.N. peacekeeping was born during this period. Growing from a couple thousand “blue helmets” addressing the Suez Crisis in 1956, to more than 100,000 soldiers and police today, peacekeepers protect civilians and aid workers in some of the world’s most dangerous trouble spots.
The U.N. also delivers humanitarian assistance to victims of war and disasters, and tries to prevent and resolve conflicts. More recently, it has taken on climate change and eradicating extreme poverty.
“The world is changing and the U.N. has to change and adapt with it. We cannot be static," Kofi Annan said.
Eight men have led the U.N. since 1945. Next year, a new secretary-general will be elected. Many say it is time for a woman.
There also are calls for organizational reform, particularly in the Security Council, where five countries hold veto power.
“The one thing everyone can agree about is that the Security Council, as it was framed in 1945, no longer represents the power structure of the year 2015," said Tom Weiss from the City University of New York.
Doyle says emerging powers want a seat at the table, and elected council members want more respect.
“The absence of a larger role of India, of Brazil, of Japan, of Germany - and one could go on - is significant. There are times at which the elected 10 feel like, as they call themselves, tourists rather than players," he said.
To stay relevant the U.N must evolve.
“However, unless there are some major shakeups, some major structural reforms, that the institution will become more and more marginal, it will become more of a historical relic," said Weiss.
But many observers agree it is difficult to imagine today’s world without the United Nations.