It was one of the defining images of 2015: small boats crowded with migrants making a perilous bid to reach Europe.
More than 1 million people arrived by sea during the year, according to estimates by the United Nations refugee agency, one of the biggest migration waves to hit the continent since the end of World War II.
At least 3,770 died or went missing in the attempt, the International Organization for Migration said Thursday. But as the year drew to a close, the boats were still coming with nothing to suggest that the flood would be stanched anytime soon.
The crisis has exposed deep rifts among the European Union's 28 members, which have struggled to respond amid acrimonious bickering and finger-pointing. Many have set up temporary border controls, threatening one of the bloc's cherished achievements: the free movement of citizens across most of its internal borders.
Here is a look at what is driving the crisis and what the new year may hold for Europe's migrants.
What lies behind the rise in the numbers?
The surge was driven by Syrians, many of whom have lost hope that the war that has torn apart their country will be brought to an end. They make up nearly half of the migrants who arrived in Europe in 2015, according to the latest estimates.
In nearby countries, to which more than 4 million refugees from Syria have fled, conditions are increasingly desperate. Few refugees are allowed to work legally in Lebanon, Jordan and Turkey, and humanitarian agencies say their appeals for more aid are not being met.
Other long-standing conflicts have also contributed to the chaotic influx in Europe, with Afghanistan accounting for about 21% of arrivals and Iraq 7%.
Around the world, nearly 60 million people have been forced to flee their homes because of war, conflict and persecution, the highest number ever recorded, according to the Office of the U.N. High Commissioner for Refugees.
Where are the migrants going?
The overwhelming majority of those trying to reach Europe — more than 844,000, the U.N. says — cross the Aegean Sea from Turkey to nearby Greek islands. But most don't stay, preferring to move on to wealthier destinations to the north.
Germany has received nearly 1.1 million asylum seekers — more than any other EU nation. They include large numbers of Europeans arriving overland from the Balkans.
Some poorer European nations have accused Germany of fueling the crisis with its open-door policy and have tried to curb the influx by dispatching troops to their borders and throwing up miles of fences. As the migrants keep coming, even Germany and other wealthier countries, such as Sweden, have introduced border checks to regulate the entry of asylum seekers.
Although such controls are allowed in an emergency under European rules, they have been fiercely criticized by EU officials and human rights groups, which have called on the bloc to uphold its values of compassion and meet international obligations to provide sanctuary to those fleeing war and persecution.
However, many people in Eastern and Central Europe agree with Hungarian Prime Minister Viktor Orban that most of the migrants are seeking better economic opportunities rather than fleeing war, and believe that they, as Muslims, will undermine Europe's Christian identity. Fear and hostility toward the migrants have spread since the discovery that at least two of the Islamic State gunmen who killed 130 people in Paris on Nov. 13 posed as refugees to travel from Syria to Europe.
Virginie Guiraudon, an immigration expert at the Center for European Studies at Paris' Sciences Po university, said the crisis revealed a fundamental misunderstanding by major EU powers about the bloc's newest members.
"They thought that these countries would remain tame and controllable and would just be happy that they were allowed in," she said. "This ignores the fact that these countries also have domestic opinions, also have domestic party politics and their own agenda."
What is Europe doing to resolve the crisis?
In an attempt to ease the burden on frontline states such as Greece and Italy, Germany tried to persuade all EU members to accept a share of refugees. Those efforts largely failed. Just over 200 people have been relocated so far.
The focus has now shifted to finding ways to discourage the migrants from embarking on the dangerous journey to Europe — and to ensure that those who reach Europe are systematically registered and vetted.
EU leaders promised in November to give Turkey more than $3.2 billion in return for help stemming the flow. But at their last summit of the year in December, the leaders failed to take action on another proposal, by the bloc's executive arm, to set up a new border and coast guard service to bolster security at entry points.
The plan has revived fears among some members, including Poland, about a loss of sovereignty to EU bureaucrats in Brussels. Still, members agreed to "rapidly examine" the proposals with the goal of reaching an agreement by mid-2016.
Is peace possible in Syria?
The crisis in Europe has renewed interest in finding a diplomatic solution to the war that has killed more than 200,000 people in Syria, caused vast destruction and left much of the country in the hands of hard-core Islamist militants.
Russia's air campaign on behalf of President Bashar Assad's government hasn't helped matters, in the view of the U.S., which heads a coalition that has been carrying out airstrikes against Islamic State in Syria and neighboring Iraq. One of Syria's top rebel leaders, Zahran Alloush, was killed in a Dec. 25 strike for which Assad's government claimed responsibility, but for which insurgents blamed Russia.
The U.S. has its concerns about Alloush's Islam Army, which is part of a rebel alliance with links to Al Qaeda. But State Department spokesman Mark Toner said he had been participating in the talks to bring about a cease-fire and a meaningful political dialogue in Syria.
"It doesn't send the most constructive message to carry out a strike like that," Toner told reporters in Washington.
U.N. mediator Staffan de Mistura plans to convene representatives of the Syrian government and opposition groups for another round of talks in Geneva on Jan. 25.
But the negotiators face enormous questions: How to decide the fate of Assad? What armed groups should be represented at the talks? And how to persuade the numerous countries that have been drawn into the war, including archrivals Iran and Saudi Arabia, to cooperate?
The answers will probably prove no less elusive in 2016 than in 2015.