Factors cited as immediate triggers or causes of the sudden and massive increase in migrant numbers in the summer of 2015 along the Eastern Mediterranean and Western Balkan route (Turkey-Greece-Macedonia-Serbia-Hungary) include: On 18 June 2015 the government of Macedonia announced that it was changing its policy on migrants entering the country illegally.
Som faktorer, der var medvirkende til at udløse den pludselige og massive stigning i antallet af migranter i løbet af sommeren 2015 langs det østlige Middelhav og vestlige Balkanrute (Tyrkiet-Grækenland-Makedonien-Serbien-Ungarn) nævnes blandt andet: at i midten af juni 2015 meddelte regeringen i Makedonien, at man ville ændre politik over for flygtningenes ulovlige grænseovergang.