There is very little chance of anyone successfully getting up to terrorism if society is
a) riddled with informers b) detaining people without charges is legal c) totalitarian ideology and political supremacy makes the establishment of parallel societies impossible. Border controls make importing terrorists next to impossible.
The former eastern Bloc had no terrorist incidents. Pulling them off would be harder, the state would cover it up, etc. Just like it had practically no mob.
It did have a great many terrorists, mostly in various training camps.