A nuclear conflict between India and Pakistan remains one of the most feared scenarios in international relations. These two neighboring countries have fought several wars since their partition in 1947, and their longstanding dispute over Kashmir has brought them dangerously close to conflict multiple times. Both nations are nuclear-armed, making any escalation particularly perilous. A hypothetical nuclear exchange would not only devastate South Asia but could trigger dire global consequences.

Most experts agree that a nuclear war between India and Pakistan would likely not begin with nuclear weapons. Instead, it would probably start with a conventional skirmish, such as the events currently occurring over the recent terror attack in Kashmir, escalating rapidly. A terrorist attack blamed on Pakistan-based groups, similar to the 2001 Indian Parliament attack or the 2019 Pulwama bombing, could trigger massive Indian retaliation. Fearing overwhelming defeat, Pakistan, with its relatively smaller conventional forces, has doctrinally hinted at the early use of tactical nuclear weapons to defend its territory.

India’s declared nuclear policy is “No First Use” (NFU), meaning it would not use nuclear weapons unless first attacked with them. Pakistan, however, has no such formal commitment. The lack of symmetry in nuclear doctrines increases instability and lowers the threshold for nuclear use.

Nuclear scenarios between the two countries would likely follow this pattern:

• Limited First Use: Pakistan might deploy tactical (small-yield) nuclear weapons against advancing Indian military columns. India, in retaliation, could respond with full-scale nuclear strikes on Pakistani cities, consistent with its doctrine of “massive retaliation.”
• Full-scale Exchange: If escalation is uncontrollable, both nations could target major urban centers. Cities like Karachi, Lahore, Islamabad, New Delhi, Mumbai, and Bangalore could be prime targets.
• Casualties and Immediate Impact: A limited exchange involving 100-150 nuclear weapons (only a fraction of their combined arsenals) could kill 50–125 million people within hours or days. Blast effects, fires, and radiation would destroy infrastructure, overwhelm medical systems, and cause mass displacement.

It should be noted that, in the recent crisis, Pakistan at first said it would give a measured response to any attack by India, but it quickly changed its statement to say that an attack by India would result in a massive retaliation.

In the event of nuclear use, the environmental effects would be catastrophic. A study published in Science Advances suggests that even a “small” regional nuclear war could inject millions of tons of soot into the upper atmosphere. This would block sunlight, cool the Earth’s surface (“nuclear winter”), shorten growing seasons, and lead to global famine, potentially killing hundreds of millions more.

Atmospheric models predict that temperatures could drop by 1.5°C to 3°C globally for several years. Monsoons critical for agriculture in Asia and Africa could be disrupted. Fisheries could collapse. The world economy, already fragile in many areas, might spiral into depression.

Other experts dispute the severity of such an exchange, especially in such a limited war that would happen between States like India and Pakistan. However, most all experts agree that there will be significant human, economic, and environmental consequences no matter what size a nuclear attack is.

Politically, a nuclear exchange would destabilize global security regimes. Nations around the world might reconsider their nuclear postures. Non-proliferation efforts could suffer serious setbacks, and the global order could tilt toward greater militarization and fragmentation. While the U.S. attacks on Hiroshima and Nagasaki demonstrated the devastation of nuclear weapons, it did not cause nations to reject the weapon but rather embrace it. A nuclear war between India and Pakistan may not usher in a era of nuclear weapon rejection as some would hope.

In the immediate aftermath or a nuclear war between India and Pakistan, surviving governments both countries — if functional — would face monumental tasks: maintaining order, feeding populations, controlling disease outbreaks, and navigating international isolation. International intervention would likely be necessary, but the effectiveness and coordination of such efforts would be uncertain amidst global chaos.

Despite repeated crises, India and Pakistan have developed some risk-reduction mechanisms, including hotlines between military leadership and regular diplomatic dialogues. International actors like the United States, China, and Russia also frequently intervene to de-escalate tensions. However, in this case, it seems major third party States have not come forth to mediate. The U.N. have issued statements urging calm, but these statements are generally ineffective.

A nuclear war between India and Pakistan would be one of humanity’s worst catastrophes — regional destruction cascading into global suffering. While it still remains a low-probability event, events are currently considered unstable. The DEFCON Warning System urges the public to maintain awareness of the current situation and to always be prepared in the event of an emergency.