Recent conflicts have challenged a traditional view of nuclear deterrence, which proposes that no entity would launch an attack, nuclear or otherwise, on a nuclear state for fear of that state’s retaliatory power. Since Russia’s full-scale invasion of Ukraine, neither Russia’s nuclear arsenal, the largest in the world, nor President Vladimir Putin’s repeated allusions to potential nuclear escalation, have deterred Ukraine from striking Russian military bases and cities .Earlier last year, Iran also struck members of a Sunni militant group operating in Pakistan, another nuclear state. In each of these cases, the ultimate weapon, thought to be the ultimate deterrent, appeared to carry little threat.

The nuclear shadow has prevented large-scale conflict between nuclear powers. Fear of mutual destruction, for example, helped prevent the Cold War between the Soviet Union and the United States from progressing into direct confrontation. After both sides tested nuclear weapons in 1998, decades of deadly clashes between India and Pakistan were reduced to a low-key conflict followed by minor skirmishes.

But nuclear arms have long had a spotty track record when it comes to deterring conflict between a nuclear state and a nonnuclear one. There are extensive drawbacks to using nuclear weapons, including their very destructiveness—which could undermine larger objectives or complicate battlefield operations—and the international backlash that would follow. Since World War II, many nonnuclear states have recognized that their nuclear adversaries face such constraints and have thus felt emboldened to attack, correctly surmising that inflicting significant casualties on a nuclear power and even taking some of its territory would not trigger nuclear retaliation. Short of a large-scale threat to its homeland or the collapse of its military, a nuclear-armed state will likely remain reticent to deploy nuclear weapons.In these scenarios, the most powerful weapons ever built confer limited practical advantages.

CAUSE AND EFFECT States considering nuclear strikes confront an array of obstacles, regardless of whether their opponents have nuclear weapons. The destructiveness of even modest-yield nuclear weapons, particularly those detonated on or near the ground, can compromise grander plans; it makes little sense to destroy an area if the goal is to acquire it, take its resources, or liberate its population. Furthermore, the fallout of nuclear strikes against a neighbor could quite literally blow back to harm the attacking state. In some cases, strikes could complicate conventional military operations by contaminating the battlefield