The globe’s nuclear safety net is fraying badly. Dangers of nuclear confrontations are growing not only in Europe, with decisions by the presidents of both nuclear superpowers, Donald Trump and Vladimir Putin, to withdraw from a treaty banning intermediate-range missiles; they are suddenly rising, too, in Asia, where India and Pakistan — both nuclear powers — have carried out conventional airstrikes across the Kashmir divide. Elsewhere in Asia, negotiations between Mr. Trump and North Korea’s leader, Kim Jong-un, to begin a denuclearization process have abruptly ended. The thickest, weight-bearing strands of this safety net are treaties that have been cast aside without being replaced. With diplomacy sidelined, policymakers are left with nuclear threats to deter competitors. But deterrence rests on the underlying possibility of the use of nuclear weapons; otherwise, they would cease to deter. This can lead to tragic miscalculations. Treaties, by contrast, muffle and reduce threats. So “strengthening” deterrence without treaties and diplomacy is dangerous; it’s a recipe for threatening your way into tight corners, as India and Pakistan have again shown.