On the 80th anniversary of the atomic bombing of Hiroshima, there is renewed focus on nuclear weapons in international security. China and other nuclear-armed states within Australia’s extended region are expanding their arsenals, with little to no arms control measures in place. This is intensifying Australia’s reliance on extended nuclear deterrence from the United States, though nuclear threats to Australia remain less acute than those to Japan or South Korea.

This new nuclear era is more dangerous than the relatively straightforward deterrence dynamics of the Cold War: today, there are more nuclear players, and interactions between them are more complex. Threats of nuclear use are on the rise, particularly from Russia and North Korea—countries that are cooperating more closely with each other and with China. Their declared thresholds for nuclear use appear to be lowering and are being deliberately blurred.

Despite this nuclear resurgence, recent regional conflicts and clashes in the Middle East, eastern Europe and South Asia have highlighted the limitations of nuclear weapons as a deterrent to conventional conflict. It is also becoming harder for states to pursue nuclear armament covertly. Longstanding assumptions about nuclear weapons and deterrence are being tested and reforged in the crucible of regional wars. While existing nuclear powers are likely to see continuing security benefits from such weapons, aspirant states will be more cautious about going down the nuclear path if they perceive the costs as outweighing the benefits. And the barriers to nuclear breakout in democratic nations such as South Korea ^[1] and Japan are too readily overlooked.

In June, Iran faced a barrage of military strikes against its nuclear infrastructure by Israel and the US ^[2]. These strikes aimed to prevent—not pre-empt, as Israel has claimed—the diversion of fissile material for weapons. This distinction matters, because pre-emptive attacks apply only when an attack is imminent. This concerted and controversial Israeli and US military action has set back Iran’s nuclear capacities significantly, though it has not eliminated them.

While Iran is unlikely to abandon its nuclear ambitions and could even be emboldened by the strikes to redouble its efforts, its pathway to reconstituting a home-grown bomb appears arduous. Reports have stated ^[3] that Iran failed to remove its enriched uranium stocks from underground sites before they were struck by specialised munitions dropped from US B-2A stealth bombers. If these stocks are now buried deep under rubble, attempts to recover them are likely to be detected, potentially triggering repeat strikes by Israel or the US. Restarting enrichment operations would take time and carry a high risk of further intervention.

Israel appears methodically determined to preserve its nuclear monopoly in the Middle East, attacking nuclear sites in Iraq in 1981, Syria in 2007 and now Iran, enforcing its red line through military force and clandestine disruption. More surprisingly, given President Donald Trump’s aversion to military entanglements, the US has actively committed its unique capabilities to further degrade Tehran’s nuclear potential. While the jury remains out whether Iran’s nuclear calculus has fundamentally shifted, Tehran has paid a significant price for pursuing its latent nuclear weapons program short of a tested capability. The regime is now in a much-weakened strategic position—hardly an attractive model for potential proliferators to follow.

At the other end of the spectrum, Russia possesses a vast and established nuclear arsenal. Since he launched his all-out invasion of Ukraine in February 2022, President Vladimir Putin has repeatedly issued nuclear threats. These threats are widely credited with deterring direct outside military intervention to help defend Ukraine.

Since the start of the invasion, however, Russia has experienced attacks against the homeland that would have been unthinkable against the Soviet Union during the Cold War. Kyiv has struck military targets deep inside Russia, including strategic bombers in Siberia, and conducted a prolonged ground incursion into Kursk. These are the first military attacks on Russian soil since the defeat of Nazi Germany, and since Russia became a nuclear power in 1949. It is a scenario few strategists would have believed possible before 2022, because it was widely assumed that no state would risk nuclear retaliation by attacking Russia directly.

While Russia has rained down ballistic missiles and other munitions on Ukrainian cities and frequently rattled its nuclear sabre, it has not used its nuclear weapons throughout the three-year conflict. Ukraine has overturned some cardinal assumptions about nuclear deterrence and strategic risk tolerance despite having no nuclear weapons of its own. There are lessons in this for other states facing armed aggression from nuclear powers.

Closer to home, India’s retaliatory air strikes on Pakistan and the latter’s response, in 2019 and on a larger scale in 2025, have underscored that nuclear weapons have not eliminated conventional conflict between nuclear-armed adversaries. India appears determined to challenge any sense of impunity that Pakistan’s nuclear weapons could impart to terrorist groups operating under state protection. This year’s round of tit-for-tat exchanges ^[4] between India and Pakistan have shown that the stability-instability paradox—the idea that higher nuclear stability may worsen conventional instability—continues to evolve dynamically and somewhat precariously in South Asia.

Of course, nuclear weapons still have strategic utility even when they are not used. Nuclear deterrence is in active operation to this very end. The fact that no state has resorted to attacking another with nuclear weapons since their first and only use in anger is one of the most surprising constants of international security since 1945. Yet the taboo on using nuclear weapons is at risk of eroding.

In our region, China’s rapid nuclear weapons build-up is not subject to any arms control to temper it, nor are North Korea’s nuclear or missile programs constrained by negotiated agreements. Beijing, Pyongyang and Moscow appear to see shared benefit in using their nuclear forces to deter external intervention in limited wars. In this context—and given China’s lead in conventional missiles, some of which are nuclear capable—the US has realised that it needs to introduce greater flexibility ^[5] into its nuclear posture to maintain credible deterrence. Plus, Washington faces the alarming prospect of fighting several nuclear-armed adversaries.

These strategic pressures are likely to precipitate demands for Australia to more actively support the US nuclear umbrella, even though Canberra faces a less immediate set of nuclear threats compared with Japan or South Korea. India’s nuclear weapons also count in the regional strategic balance with China, a fact that could eventually insinuate itself into the Quad’s underlying rationale, however uncomfortably. For similar reasons, AUKUS may reluctantly have to put out nuclear feelers ^[6] in future, in spite of its conventionally-armed framing.

Australia is no stranger to nuclear matters, but Canberra’s past efforts have been mostly confined to diplomacy ^[7] in support of non-proliferation. In this tougher and less predictable era, Australia’s nuclear security interests are also rising but are likely to remain indirect in the form of enhanced support for US extended nuclear deterrence. This will still require greater understanding of nuclear weapons, concepts for their employment, and the interplay with conventional war—all factors that strengthen the need for Australia to nurture a new generation of nuclear expertise appropriate for tomorrow’s needs.