Ancient Macedonia was the starting point for the epic of Alexander the Great and the creation of Hellenistic civilisation which the Greeks consider one of the most glorious chapters in their history. The creation of a new state bearing the name of Macedonia (which is also the name of a Greek province) was seen as usurping this historical heritage - especially since some Macedonian nationalists are disputing that Alexander the Great was a Greek. The name has therefore become the touchstone of Greco-Macedonian relations.
Then there was the question of the new state’s flag, which bore the star of Vergina, a design found on the tomb of Alexander’s father, Philip II. For the Greeks, this was a confirmation of how their heritage was being usurped and evidence of irredentist Macedonian plans - Vergina, where the tomb was discovered, is in the Greek province of Macedonia.