These migrations caused the koinéisation of the Shtokavian dialects, that used to form the West Shtokavian (more closer and transitional towards the neighbouring Chakavian and Kajkavian dialects) and East Shtokavian (transitional towards the Torlakian and the whole Bulgaro-Macedonian area) dialect bundles, and their subsequent spread at the expense of Chakavian and Kajkavian.