<P> Recent history is discussed in the articles history of human migration and human migration . </P> <P> When people cross national borders during their migration, they are called migrants or immigrants (from Latin: migrare, wanderer) from the perspective of the country which they enter . From the perspective of the country which they leave, they are called emigrant or outmigrant . Sociology designates immigration usually as migration (as well as emigration accordingly outward migration). </P> <P> As of 2015, the number of international migrants has reached 244 million worldwide, which reflects a 41% increase since 2000 . One third of the world's international migrants are living in just 20 countries . The largest number of international migrants live in the United States, with 19% of the world's total . Germany and Russia host 12 million migrants each, taking the second and third place in countries with the most migrants worldwide . Saudi Arabia hosts 10 million migrants, followed by the United Kingdom (9 million) and the United Arab Emirates (8 million). </P> <P> Between 2000 and 2015, Asia added more international migrants than any other major area in the world, gaining 26 million . Europe added the second largest with about 20 million . In most parts of the world, migration occurs between countries that are located within the same major area . </P>

Name one factor that can lead a refugee to leave his country