MOSCOW — The expulsion of scores of Russian diplomats from the United States, countries across Europe and beyond has raised, yet again, the question of whether the world is veering back where it was during the Cold War. The alarming answer from some in Russia is: No, but the situation is in some ways even more unpredictable.

For all the tension, proxy conflicts and risk of nuclear war that punctuated relations between Moscow and the West for decades, each side knew, particularly toward the end of the Cold War and collapse of the Soviet Union in 1991, roughly what to expect. Each had a modicum of trust that the other would act in a reasonably predictable way.

The volatile state of Russia’s relations with the outside world today, exacerbated by a nerve agent attack on a former spy living in Britain, however, makes the diplomatic climate of the Cold War look reassuring, said Ivan I. Kurilla, an expert on Russian-American relations, and recalls a period of paralyzing mistrust that followed the 1917 Bolshevik Revolution.

“If you look for similarities with what is happening, it is not the Cold War that can explain events but Russia’s first revolutionary regime,” which regularly assassinated opponents abroad, said Mr. Kurilla, a historian at the European University at St. Petersburg.