The war in Kashmir has never been about taking and holding territory. No militant group can defeat an army at that. The tactics have always been about causing harm to the enemy. India feels it has to have a police and military presence in Kashmir. Constant attacks on those forces and the infrastructure that supports and houses those forces has frustrated the Indian army to such a degree in the past they stopped holding some territory where they felt the cost of holding it was too much. If you stand against a giant like the Indian army and try to go toe to toe, you will be defeated but geurilla tactics have been successful against all occupation forces around the world.
I don't think situation is that black and white.
Militant organizations such as ISIS, Taliban and Mahdi Army - during their hayday - comprised of highly trained and battle-hardened soldiers and were heavily armed and disciplined enough to challenge a conventional army in the battlefield.
Some examples:
1. TTP (under leadership of Baitullah Mahsud) was able to contend with Pakistan Army in Waziristan to the extent that it was able to defeat Pakistan Army in a number of pitched battles. TTP lost that kind of effectiveness when US assassinated Baitullah and it fractured in the aftermath.
2. Taliban captured much of Afghanistan during its war against Northern Alliance (comprised of groups that were able to contend with the Red Army in Afghanistan earlier).
3. ISIS (easily) defeated the new Iraqi Army in-spite of its resourcefulness (equipment and manpower) and managed to capture large swaths of territory in Iraq and Syria. In Syria, Syrian Army was not able to stop advances of ISIS.
4. Mahdi Army turned several cities in Iraq into fortresses/no-go areas.
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US military machine has unparalleled power projection and its counter-terrorism capabilities are truly formidable. American forces toppled Taliban from power in Afghanistan in a span of 2 months, defeated Al-Qaeda network in Afghanistan and Pakistan in a span of 9 years, defeated Mahdi Army in Iraq in a span of 3 years and are now hammering ISIS in Afghanistan, Iraq and Syria. US forces also have assassinated a large number of militants in Pakistan (including the feared Baitullah Mahsud) via state-of-the-art drones, softening their resistance and making it easier for Pakistan Army to defeat them. However, this is not to say that only US is good in asymmetric operations:
1. German Wehrmacht soundly crushed state-wide Polish resistance movement during WW2 even though it was very well organized and severe.
2. The original Iraqi army (under Saddam Hussein) effectively neutralized uprisings in Shia and Kurd dominated regions in Iraq in 1993.
3. Sri Lankan armed forces completely eliminated Tamil Tigers in a span of 30 years.
Therefore, performance of a militant organization in the battlefield depends upon what kind of foe it is up against and its own capabilities. Similarly, every army does not have a potent counter-terrorism capability.
Indian Army might have suffered significant losses in Kashmir but it continues to endure. Though resistance in Kashmir is insignificant when compared to what US forces encountered in Afghanistan and Iraq and what German forces encountered in Poland.