Ghanaian diplomat Kofi Annan spoke about the continuing campaign for peace when he appeared at Cheltenham's Literature Festival.
Speaking on the opening night of the 10-day festival, the man who served as the seventh Secretary General of the United Nations argued that in order to remain of value, the international agency had to realise that the great powers of 1945 were not the great powers of today.
He said some of the smaller countries could currently "pretend' they had the same powers when they were able to join the UN council temporarily, but the five permanent member states still held the power of veto.
He said: "It's like pretending countries like Ghana, Togo, Costa Rica can sit on the council and carry the same weight."
Speaking with The Times' James Harding, the 74-year-old who named Nelson Mandela as his ultimate inspiration for peace, admitted he feared there would be thousands more deaths in Syria.
"It is a very difficult situation," he said.
"We have to make sure the reforms can be held together for the Syrian people."
He spoke about the "special relationship" between the US and the UK over Iraq, and how other UN countries had been left "baffled" by the UK's decision to support the US and invade Iraq. He also admitted that the UN had failed Rwanda in the 1993 genocide.
He addressed the topic of disillusionment over the effectiveness of international aid, adding that discussions were ongoing to encourage countries such as China and India to voluntarily give up funding they received for HIV/Aids, and so leave more money for others.
When asked by an audience member how he managed to keep himself going, Mr Annan said: "It's extremely difficult. At the beginning it was much harder but you learn to understand that as a leader and secretary general you have to lead staff and send a message of hope to the rest of the world. You cannot allow these painful situations to eat you up."