First off let me say, any war between the two would be extremely bloody. Both sides know this, so a major war is highly unlikely.
So everything I’m writing here is in the extremely unlikely event than China and India decide to try and wipe the other off the map, and are willing to put their entire nation and many years towards the effort.
If either side did decide to engage in a major war with the other, China would probably win. Here’s my reasoning.
A war between China and India that lasts long enough to redraw the border in any significant way would take years. There’s no way around that, the terrain is just too rough for blitzkriegs and sudden movements.
The longer wars go on, the less it becomes about clever strategies and generals fighting each other, and the more it becomes a battle between nations. The ability to produce more tanks, shells, rifles, bullets and soldiers than the other side.
The Chinese economy is over twice as large as India’s. Also manufacturing is a larger part of China’s economy than India, accounting for around 50% of China’s economy compared to around 20% of India’s.
In a long conflict where both the countries gear for war, this means that for every shell, bomb and bullet that India fires at China, China fires four or five back at them.
Also, the majority of Chinese industry is quite far from India, and hard to damage as a result. But a lot of Indian industry is within striking range of China. So China would have an easier time than India at damaging the other side’s ability to wage war.
Some other factors I think might be important are that the Indian-Chinese border is not Iraq. Iraq is pretty flat and open. You can’t move your troops in Iraq without a technologically sophisticated enemy being able to see them from air, space or with radar from HUGE distances. In a mountainous region, especially one with lots of trees, you’re not going to be able to see anywhere near as much from the air or from space. High tech sensors won’t be as important. The ability to see and hit things 5kms away won’t be relevant when you’re rarely see more than 1km without a hill, ridge or tree in the way.
Look at Bosnia for an example. It’s a very mountainous region covered with trees. They faced NATO attack from the air for three months, yet NATO couldn’t even completely stop the Bosnian air-force from flying. By flying low down in the mountains, the Bosnians found they could make brief flights. And at the end of the three month campaign, the vast majority of the Bosnian ground forces came out of hiding completely intact.
So tactical air attacks and tactical reconnaissance would be fairly unimportant roles for the air-forces of both sides. Strategic attacks and reconnaissance would be a different matter. Striking at each other’s industry, dams, bridges, roads, etc would probably more effective.
As for reconnaissance. Tactically due to the limited ability to see far, you can’t rely on the ability to spot a vehicle, platoon or company. There’s just way too much nature in the way. But on the large scale, spotting the movement of Armies and Army Groups, reconnaissance would be vital.
The border between the two nations is very long. A quick estimate on a map gives me around 1,000kms. Concentrating 8 million men on a 100km section would be a likely strategy. Strategic reconnaissance would be needed to spot this before it happens. Could either side’s air defences and anti-satellite defences actually reduce the other sides ability to spot what’s going on for long enough for a surprise attack? I’m not sure.
Also if we are talking a large scale long term war, then both side’s armies are going to grow huge. 20+ million men isn’t ridiculous. if you’ve got an army that big, then having hundreds of thousands, maybe up to a million of them acting as engineers is very possible. Even the Himalayas become a lot more traversable when you have that many engineers working for years building tunnels, bridges and roads.
As for logistics, yes now neither country could project enough force far enough to completely defeat the other side, but in a hypothetical major longer term war between the two, both sides could buy or build huge numbers of trucks, trains or whatever else then need to move supplies.
In the end, if India managed to conquer half of China it would probably be the southern and western region. This would impact China’s ability to make war, but not destroy it. However if China managed to conquer half of India, it would be the northern region. This would severely impact India’s ability to make war, and would probably make the war unwinnable for India. If you could ever call having a war that destructive winnable.
So on that basis, the war would be easier for India to lose than for China to lose.
If China loses an army in a strategic mistake or due to great Indian plans, they could replace the losses, especially the weapons an vehicles, with greater ease than India could, due to China’s much bigger industrial capabilities.
Again making any strategic defeat less of a problem for China than it would be for India.
If China lost the air war, then the lack of surprise would be a hindrance, so they’d have to resort to a war of attrition. But for the above reasons they could win such a war. Especially with their Industry being largely untouchable due to it’s location.
If India lost the air war, they just couldn’t win a war of attrition, and without strategic surprise, there’s no real room for clever Indian plans to tip he balance in their favour. Any large scale force build ups or movements would be spotted.
There’s just too many ways India could lose. For them to win they’d need to make virtually no major mistakes for year after year, while they take enough Chinese territory to knock them out of the war. Yeah, they could do it, but I’ve read enough history books to know it’s pretty impossible to run a war that long without a major setback or mistake or two.
Anyway, that’s my reasoning. Feel free to rip it to shreds and point out all the glaring errors. =)