Turning Bulgarians into Macedonians
The Slavs who settled in Macedonia owed their primary allegiance to their individual tribes and, short of an awareness of collectively being 'Slavs" (Sloveni, a people not confined to Macedonia), did not develop a specific sense of a unique ethnic identity until well into the twentieth century.
When the warlike Bulgars (originally a Tartar group) arrived on the scene in the 680's AD, they rapidly dominated the Slavs of the east-central Balkans including Macedonia's Slavs. historically all these Slavs came to be counted as 'Bulgars". The original Bulgars were rapidly assimilated by their much more numerous Slavic subjects so that little more than their tribal name survives. The modem Bulgarians are certainly a Slavic people.