This decade has seen massive movements of people fleeing war, poverty and persecution. Here are some key cases.
Since 2011: Syria
The Syrian war has killed more than 360,000 people since it began in March 2011 and it has led to a massive exodus of people, mostly to camps in neighbouring countries.
More than half the country's 23 million population has fled, with 6.6 million of those internally displaced and more than 5.6 million going abroad.
Turkey took in the biggest number, with the UN refugee agency UNHCR registering more than 3.6 million there, followed by Lebanon with less than a million (Beirut says it is 1.5 million) and Jordan with 673,000 (1.3 million according to Amman).
Hundreds of thousands of Syrians have also fled to Europe, and most notably to Germany.
2013-2018: South Sudan
Independent since 2011, South Sudan became mired in civil war in 2013 that lasted five years and left more than 380,000 people dead and forced some 4.2 million people a third of the population to flee.
The UNHCR says nearly 2.2 million have left the country and are now spread across neighbouring countries in Uganda (785,000), Sudan (764,000) and Ethiopia (422,000).
The massive and regular arrival of migrants via the Mediterranean and into Europe over recent years has provoked a major crisis in the bloc with some member countries adopting particularly tough new measures.
After a peak in 2015 of more than one million migrants landing on Europe's shores from the Mediterranean, the numbers have dropped to more than 362,000 in 2016, 172,000 in 2017 and 132,000 since the start of 2018.
Of those who have arrived in 2018, 108,400 have reached Europe by the sea, according to the International Organization for Migration. Some 2,130 died making the journey.
There have been some flashpoints, including the controversy over the 629 migrants aboard the Aquarius rescue ship stranded in the Mediterranean after Italy and Malta refused to let it dock.
Policy on migration has been one of the major points of friction between countries in the bloc.
Since 2015: Venezuela
The United Nations says some three million Venezuelans are now living abroad, 2.3 million of whom have moved since 2015, fleeing the country's severe economic, political and social crisis.
Neighbouring Colombia, which shares a border of 2,200 kilometres (1,367 miles) with Venezuela, has taken in the most, around one million, followed by Peru (at least 550,000) and Ecuador, with around 300,000.
The exodus of the Venezuelans is, according to the UNHCR the most massive displacement of people in recent Latin American history.
A caravan of thousands of migrants mostly from Honduras left the Central American country to escape violence and poverty and by mid-November, they had reached the US border.
Other caravans coming from Central America joined them and other migrants travelled by foot and hitchhiked to cover the thousands of miles in the hope of being granted the status of refugee in the US.
Some 6,000 people gathered in the Mexican city of Tijuana but were unable to cross the border after US President Donald Trump deployed thousands of soldiers who forced a number of migrants to turn back.
This decade has seen massive movements of people fleeing war, poverty and persecution.