Yes it is. They are Slavs.
"In broadest definition, there are 28 countries that constitute the region of Eastern Europe: Albania, Armenia, Azerbaijan, Belarus, Bosnia and Herzegovina, Bulgaria, Croatia, Cyprus, the Czech Republic, Estonia, Georgia, Greece, Hungary, Kazakhstan, Kosovo, Latvia, Lithuania, Moldova, Montenegro, North Macedonia, Poland, Romania, Russia, Serbia, Slovakia, Slovenia, Turkey (East Thrace), and Ukraine, all of which can be classified into any of the 6 categories below."
https://en.wikipedia.org/wiki/Eastern_Europe
With the possible excception of Hungary and Slovenia all of these are problem nations.