Short answers, pulled from the story.
Immigration is the international movement of people to a destination country of which they are not usual residents or where they do not possess nationality in order to settle as permanent residents. Commuters, tourists, and other short-term stays do not fall under this definition.
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 live in just 20 countries.
The United States hosts the largest number of international migrants 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.
The term immigration was coined in the 17th century referring to non-warlike population movements between the emerging nation states.
Immigrants are motivated to leave for reasons including a lack of local access to resources, a desire for economic prosperity, family reunification, escape from prejudice or conflict, and climate or environmentally induced migration. Natural disasters can amplify poverty-driven migration flows.