Europe is experiencing what many consider to be its worst migration and refugee crisis since World War II, as people flee conflict and poverty in neighboring regions. Many are from the Middle East and Africa; others come from Ukraine,as well as Kosovo and elsewhere in the Western Balkans. Experts have characterized the influxes as mixed migration, defined as flows of 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. Sometimes termed irregular migrants, these individuals do not have the required documentation, such as passports and visas, and may use smugglers and unauthorized border crossings.