From the Document: "Over the past several years, Europe has experienced significant refugee and migrant flows as people have fled conflict and poverty in bordering regions. Although 2015 is considered the height of the crisis, refugee and migrant arrivals have continued (see Table 1). The war in Syria has created millions of refugees in neighboring countries and driven some to leave for Europe. Other refugees and migrants originate from elsewhere in the Middle East, as well as Afghanistan, Africa, South Asia, and some Western Balkan countries. Experts characterize these flows as 'mixed migration', defined as different groups of people--such as economic migrants, refugees, asylum-seekers, stateless persons, trafficked persons, and unaccompanied children-- who travel the same routes and use the same modes of transportation (see text box). Many of these individuals do not have the required documentation, such as passports and visas, and often use smugglers and unauthorized border crossings."
CRS In Focus, IF10259
Congressional Research Service: https://crsreports.congress.gov/