The author (who grew up in Poland while it was a puppet state of the USSR) offers examples literally in the same paragraph that you quoted. The full paragraph is:

Russia’s expansionist policy, on the other hand, continues to cast a long shadow across Europe. The country has a long history of conquest, but for centuries, its vast dominion resembled a loose federation of fiefdoms, not a single state; it wasn’t until the emergence of the USSR that a cohesive national identity — along with a renewed focus on global expansion — started to take hold. Through various machinations, the USSR soon ended up annexing Estonia, Latvia, and Lithuania; and seizing military and political control of Poland, Czechoslovakia, Hungary, Bulgaria, Romania, and other neighboring states. For decades, the residents of these lands suffered repression and economic hardships — and were barred from leaving the Soviet-controlled world.