BERLIN - On Tuesday, the number of refugees and migrants who arrived in Europe this year passed the 1 million mark, according to the International Organization for Migration. Here is what you need to know about one of 2015's most defining tragedies.
What caused the influx?
The war in Syria is the primary reason for the dramatic increase in refugees. Since the beginning of an uprising in 2011, millions have fled the country - many to Lebanon and other neighboring nations. An estimated 4 million Syrian refugees currently live in camps in Turkey, Jordan and Lebanon. But the number of people leaving the country began to rise even more after the government began an effort to enlist more reservists to serve in the army and eased travel restrictions.
The miserable conditions in some of the camps as international aid programs remain underfunded is another key reason for the dramatic influx into Europe, as The Washington Post's Liz Sly explained earlier this year.
Macedonia's decision to lift harsh border control measures in June also contributed to the mass flight to Europe. In recent months, however, restrictions have increased. Hungary and several other countries have built fences to prevent refugees from entering, as my colleague Adam Taylor reported.
The journey to Europe became more affordable this year. When the border restrictions were temporarily lifted this summer, more refugees chose the shorter sea crossing between Turkey and Greece (rather than crossing from North Africa into Europe). Refugees had to pay smugglers much less than if they chose the much riskier Mediterranean Sea route.
What role did Germany play?
Reactions to the influx varied widely. Sweden and Germany were perceived as Europe's most welcoming countries. German Chancellor Angela Merkel decided to let all Syrians enter the country in a landmark decision that was condemned by other European leaders, who feared it would attract even more refugees. (Legally, European Union countries are bound to send refugees back to the countries through which they entered E.U. territory.)
At Munich's main railway station, thousands of Germans applauded as refugees arrived in early September - a stark contrast to reactions in Hungary, where refugees were blocked from continuing their journey by train.
By late September, however, Germany had stopped train travel to and from neighboring Austria in order to regulate the influx.
Some refugees say they do not feel welcome in the country, where reception centers are overcrowded and authorities have been slow to process administrative details. Moreover, anti-refugee protests and arson attacks on reception centers have raised worries of a growing backlash.
What were the first signs of a backlash?
Other countries were skeptical early on: Britain, France, many Nordic countries and most of eastern and southern Europe limited their commitment to refugees.
By September, several European countries were refusing to accept quotas that bound them to host a certain number of refugees. Some of those countries began accommodating refugees under conditions decried as outrageous. Human rights advocates called the treatment of refugees in the Czech Republic inhuman. Meanwhile, even richer countries, such as Denmark, tried to discourage refugees from entering the country - cutting benefits and even launching an advertisement campaign in Lebanese newspapers to portray the country as a rather unfriendly destination.
Where is the political debate headed?
The crisis has partly been blamed for the rise of right-wing movements in several European nations. Right-wing parties had gained momentum before this year's refugee influx, but many electorates are now more divided than ever.
In Germany, the so-called "Alternative fur Deutschland" party has raised worries over a new right-wing movement in the country. But other nations have shown much clearer signs of a right turn: Poland's right regained power in October despite economic progress in recent years. Hungary's conservative Prime Minister Viktor Orban turned further to the right. In France, more people voted for the National Front in regional elections in early December than ever before.
The National Front's success appears to be the result of years of failed economic and social policies by the Socialists and conservatives. However, some French who are suffering under a lackluster economy have grown weary of having to accommodate refugees.
So far, the terrorist attacks in Paris last month have not had a decisive impact on the European refugee debate. After the Nov. 13 attacks, French President Francois Hollande pledged to welcome the refugees his country had agreed to accept.
But the mood could easily change in the event of more attacks.
Will the numbers keep growing in 2016?
Sweden has announced that it is unable to keep up its high acceptance rate, and Merkel recently said her country may be reaching its limit as well. However, the European Union still has no real plan for stopping arrivals.
"People are going to keep coming. There's only so long that millions of people will sit in a refugee camp without a livelihood," said Lani Fortier, who leads the International Rescue Committee's efforts in Lesbos, the Greek island that has become the main gateway to Europe.
Morgan Johansson, Sweden's migration and justice minister, agreed that Europe's refugee crisis will not be over anytime soon. "In the long run, Europe must face this as a union and not just single member states looking out for their own interests. Because this is not going to go away. We're going to have refugees coming here for a long time to come," he said.
The European Union now wants Turkey to stop refugees from crossing into Europe. It remains uncertain to what extent President Recep Tayyip Erdogan will fulfill his promises, though. Border fences in Eastern Europe could force some refugees to try crossing via the much more dangerous Mediterranean Sea route.
However, in that case, Europe could find itself in the same position it was in earlier this year: The near-weekly boat disasters that left hundreds of refugees dead shocked many on the continent, ultimately forcing governments to adopt a more open approach toward refugees.