More than a million refugees crossed into Europe last year, sparking a crisis as countries struggled to cope with the mass influx.

War-torn Syria continues to be the biggest driver of migration, but refugees are also fleeing unrest in countries such as Afghanistan, Kosovo and Iraq.

The World Economic Forum's Global Risks Report 2016 looks at the most pressing global risks facing the world, and how they could evolve and interact in the next decade. Top of the list of risks of highest concern for the next 18 months in this year’s report, by a considerable margin, was large-scale involuntary migration.

In Davos this week, world leaders talked extensively about the plight of refugees, and what this means for the future of the union.

1. Greek Prime Minister Alexis Tsipras

"When it comes to the refugee issue, what is happening in the Aegean as we speak is a great shame for our common European culture and civilization. People are losing their lives in the Aegean Seas because traffickers are working there unimpeded."

2. Mario Draghi of the European Central Bank

"The refugees are both a challenge and an opportunity for Europe. It's a challenge for sure, and it would be foolish to ignore the size or the extent of the challenge. Our society will be changed by this. In which direction, we can only guess. It's also premature to know how long it will take to transform this challenge into an opportunity."

3. German Finance Minister Wolfgang Schäuble

"We all agree that the inflow, this influx, is too high, and we now have to concentrate on how to revert this situation. I think that what is most important is for us to invest billions into those regions from which the refugees come, to reduce the pressure on the external frontiers of Europe to make sure Europe does not become a fortress."

4. Prime Minister of the Netherlands Mark Rutte

"In the first three weeks of this year, there were 35,000 people crossing the sea from Turkey into Greece. Last year it was only 1,600 in the full month of January. Now it's 35,000 in the first three weeks, and this is winter. So when spring comes, the numbers will quadruple, they will go up considerably. We cannot as a European Union, at least for the Netherlands, for Germany and other countries, we cannot cope with this any longer, so we have to get a grip on it."

The Annual Meeting is taking place in Davos from 20 to 23 January, under the theme “Mastering the Fourth Industrial Revolution”.