India and Pakistan have fairly comparable arsenals but the danger of non-state actors gaining control of nuclear weapons is more acute in Pakistan, where militant groups have in the past attacked military facilities.

“They’ve made their point. India and Pakistan both stopped after the sixth nuclear test, but that doesn’t make either a non-nuclear power,” Lee said.

How did India and Pakistan develop their nuclear weapons programmes?

In 1965, Zulfikar Ali Bhutto, then president of Pakistan, said: “If India builds the bomb, we will eat grass or leaves, even go hungry – but we will get one of our own.”

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“The war in 1971 fuelled a sense of existential threat that was really keenly felt by the leaders in Pakistan,” said Toby Dalton, co-director of the nuclear policy programme at Washington DC’s Carnegie Endowment for International Peace. “Nukes were the solution to that existential threat.”

In 1974, India tested its first nuclear bomb, code named Smiling Buddha. However, neither country truly announced its presence as a nuclear power until a series of weapons tests in 1998, when India tested six bombs over the course of three days. Three weeks later, Pakistan detonated five bombs in a single day and a sixth three days later.

The two states both share borders with China, one of the world’s biggest nuclear powers, although the exact size of its arsenal remains unknown. Reducing nuclear asymmetry with China has been a motivating factor in India’s weapons development.

How big are their nuclear arsenals?

Though India’s conventional (non-nuclear) military forces far outstrip Pakistan’s, the two nations have comparable nuclear arsenals. The main difference is that India possesses a nuclear triad – the ability to launch nuclear strikes by air, land and sea – while Pakistan’s sea-launched cruise missiles are under development.

The Stockholm International Peace Research Institute, which compiles data on conflict and arms control, estimates India currently has between 130 and 140 warheads, while Pakistan has between 140 and 150.

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Pakistan’s missiles are longer-range, including the Shaheen-3 missile, capable of striking India’s far-flung Andaman Islands.

India in 2018 operationalised its “INS Arihant” nuclear-powered ballistic missile submarine, making it one of only six nations in the world with this capability. Pakistan has tested several sea-launched missiles.

With these arsenals, both are capable of causing massive damage to one another by hitting critical urban centres.

What are the mechanisms keeping them in check (or not)?

India and Pakistan are among the world’s nine nuclear weapons states, alongside China, France, Israel, North Korea, Russia, the United Kingdom and the US.

China has been particularly vocal in opposing nuclear proliferation in its backyard, as India and Pakistan have not signed the NPT.

“China has never admitted that India and Pakistan are nuclear weapons states,” China’s foreign ministry spokesman Lu Kang said. “China’s position on safeguarding the NPT is firm and has never changed.”

Despite non-adherence to the NPT, India has a strict “no first use” policy, although high-level officials have recently called for pre-emptive strikes to eliminate Pakistan’s nuclear capabilities.

Pakistan does not have such a policy, although Islamabad claims it possesses nuclear weapons only to deter a strike by India, its economically, politically and militarily stronger neighbour. To deter Pakistan, India relies on the threat of overwhelming retaliation.

“Though they may have driven the level of conflict down, nuclear weapons have not had a profoundly stabilising influence in South Asia,” Dalton said. “Pakistan has consistently courted low-level conflict and nukes have not enabled it to do so more than was already there.”

India and Pakistan both have safeguard agreements with the International Atomic Energy Agency regarding their civilian nuclear plants.

Why can’t India and Pakistan be models for North Korea’s nuclear development?

The exact size of North Korea’s arsenal is unknown – estimates vary between as few as 15 or as many as 60 weapons.

North Korea withdrew from the NPT in 2003 and has been conducting weapons tests since 2006, while also denying international inspectors access to nuclear sites and making threats about attacks on US territory. Its sixth and most recent test of a nuclear weapon was in September 2017.

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Having rejected India and Pakistan as nuclear weapons states, Beijing is unlikely to welcome another nuclear neighbour. However, China is North Korea’s primary trading partner and has lobbied the United Nations to lift sanctions against North Korea, which were imposed in response to its nuclear weapons programme.

North Korean officials have cited India and Pakistan as aspirational models for acceptance as a de facto nuclear state.

“When North Korea looks out at the world at other models, they want to be treated like India,” Dalton said. “They want to be accepted as a nuclear power and have normal relations with other states, not treated as a lesser power that’s a threat to the international system.”