Ever heard a communist guy named Tito,founder of Yugoslavia? Tito wanted to make a country out of smaller mostly Slavic countries. (Montengero,Serbia,Bosnia etc). In order to do that he had to make a certain group of those Slavs with really close ties to Bulgaria,believe they really did not have any ties to Bulgaria.So he came up with the idea to brainwash them into believing they were actually the decedents of ancient Macedonians and that the ancient Macedonians were never Greek.Well,he did not convince historians or the world,but he did manage to convince that group of people that although they spoke a Bulgarian dialect,had Slavic customs,folklore etc. they were the real Macedonians and that the Greeks occupied most of their previous country (Macedonia). This did not cause much trouble to us the Greeks when Yugoslavia was a unified country,but when communism fell,so did Yugoslavia.And then we had to deal with a small nation in the North who called themselves Macedonians,hated our guts,laid claim on a big chunk of Greek territory (most of the Macedonia Greek prefecture),co-opted our history,including Alexander the Great and everything he did etc. It was the reason Greece blocked their entrance to NATO for years,it was never about just a name,it was about a historically inaccurate racial and national identity which had became a threat to Greece itself.

PS.Bulgaria is pissed too with the fake Macedonians issue as well,because they see those people as a Bulgarian subgroup,which Tito managed to brainwash into believing they had nothing to do with Bulgaria.