Answer:
Three reasons for mass immigration today are better job opportunities, civil wars and famine.
Explanation:
In the 20th century (continuing into the present century), an extraordinary development of the means of communication and transport have made possible the massive migrations of people on a global scale never before seen. These are socio-economic migrations, stimulated by a process of increasing inequality between developed and underdeveloped countries and accentuated, especially in the latter case, by bad governments.
That inequality, that constitutes the basic problem, degenerates in turn into different problems. Depending on the type of crisis, they develop from lack of job opportunities, to serious structural problems such as famines and even armed confrontations.