Hardly a surprise, but just to confirm that India massively outguns Pakistan:

India’s advantage on my CMP index, an attempt to objectively quantify military power, has increased from 60% in 1988 to almost fivefold today by 2015.

Military spending (2017): India – $60 billion; Pakistan – $10 billion

This is reinforced by a quick look through military inventories on Wikipedia. India has 1,650 T-90’s and 124 Arjuns; Pakistan has ~700 equivalents (T-80UD’s and Al-Khalids). And even that won’t matter much, as India has total air dominance: It has ~300 4+ gen fighters (mainly Su-30’s and Mig-29’s) to Pakistan’s 45 4 gen fighters (F-16’s).

Historical record: India has won (to varying degrees) all of the four wars it has fought with Pakistan.

A more interesting problem is what will happen if they were to fight a nuclear war. They are about equally matched in atomic weaponry, though Pakistan has more in the way of tactical nukes, while India’s are more for balancing against China.

A classic study published in 2007 estimates there would be 12 million fatalities in India and 7 million in Pakistan if they were to exchange 50 15-kt nukes in urban strikes. That sounds about right. At current growth rates, it would take Pakistan two years and India less than a year to replenish their populations.

In this scenario, I expect Pakistan to cease to exist as a state.

There have also been many studies that even a limited nuclear war could produce catastrophic climate effects. I don’t find that too plausible. Even 100 15-kt bombs constitute just 3% of the power of the Tsar Bomba, and that didn’t really do much. You’d need all of the world’s nuclear weaponry just to equal the Mount Tambora eruption in 1815.

EDIT: Errata – chart’s left axis should say “Comprehensive Military Power (as % of US in 2000)”.