New arms race taking shape amid a pandemic and economic crisis. What could go wrong?

Three decades after the Cold War ended without a long-feared nuclear cataclysm, arms control experts are starting to think the sigh of relief heard around the world then might have been premature. In recent weeks Russian fighter aircraft intercepted U.S. strategic bombers and surveillance planes over the Black Sea and eastern Mediterranean, in one case risking a midair collision. At the same time, Moscow tested a new missile capable of destroying U.S. satellites. China recently closed its authoritarian grip around Hong Kong, threatened to “smash” any formal independence move on the part of Taiwan and announced an unprecedented show of military force with an amphibious landing exercise in the...