You say nationalist as if that's something wrong, even forbidden. Greece itself is being run by nationalist governments since decades (disregarding their political color). Austria is run nowadays by a nationalist government. Heck, the US is run by Trump, who is a nationalist.

"and expansionist government"

FYROM has never ever even hinted they, a 2.1 million people tiny nation (https://en.wikipedia.org/wiki/Demographics_of_the_Republic_o...), have any territorial request on Greece, an 11.2 million people nation (https://en.wikipedia.org/wiki/Demographics_of_Greece). As Greece is part of both the EU and NATO, the idea of an expansionist FYROM is pure and simply ridiculous.