Russia's been blatantly assassinating people across Europe for years and would invade Poland in a second for personal pleasure even if it caused an economic loss for them again.
They haven't evolved past Mongol horde methods of living with their neighbors and are relying on everyone else always taking the "rational" result of appeasing them rather than fighting back. The correct response in this iterated game is to punish them and let their more productive people immigrate to you.