World leaders meeting at the United Nations starting Monday will be trying to make progress on two intractable problems at the top of the global agenda — the biggest refugee crisis since World War II and the Syrian conflict now in its sixth year which has claimed over 300,000 lives.

Against a backdrop of rising ethnic and religious tension, fighting elsewhere in the Mideast and Africa, extremist attacks across the world and a warming planet, there are plenty of other issues for the 135 heads of state and government and more than 50 ministers to try to tackle.

U.S. Ambassador Samantha Power told reporters Thursday: "It's no secret there's a lot of fear out there." She cited Britain's vote to leave the European Union and threats from extremist groups.