There are. I think you are confusing the fact that they are often broken, without consequences for offenders, with there being no rules. It’s like saying that there is no law against burglary because there is a lot of burglaries and the vast bulk of them don’t result in prosecutions.
There are superficial legal obligations put in place, but subsequently violated by both sides.
The obligations are not superficial, as Lt Calley found out.
I don’t think that your statement can be applied as a general proposition that all sides violate all rules equally in all wars. Everything depends on the circumstances.
Several factors seem to determine the extent of observance of the rules.
The enemy’s conduct can influence how the same nation or even the same troops respond. American and Australian troops routinely shot Japanese wounded in WWII because of the Japanese habit of playing dead and then detonating a grenade or shooting or stabbing Allied soldiers when they came within range. The same practice was not used by American or Australian soldiers fighting the Germans or Italians. Unlike the Americans whose troops generally fought in either Europe / North Africa or the Pacific rather than in both theatres, the Australian 6th and 7th Divisions fought in North Africa / Middle East and the Pacific. These troops did not shoot German, Italian or Vichy French wounded but provided them with whatever assistance they could manage. The same troops routinely shot Japanese wounded when fighting in the Pacific. The same troops who routinely accepted the surrender of German, Italian and Vichy French prisoners at times shot Japanese troops attempting to surrender because they couldn’t, or didn’t want to, handle prisoners. (Accepting the surrender of Italians in North Africa mightn’t prove much. The Australians wouldn’t have had enough ammunition to shoot them all. 
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The ethnic or cultural similarity of the opponents also seems to dictate the extent of observance of the rules. It’s harder to mistreat people like us. Common German behaviour in the East was entirely different to common German behaviour in the West. In part, this probably reflects the similarity German troops felt they shared with their opponents in the West, while they tended to regard Slavs as ethnically or culturally inferior. American and Australian behaviour against the Japanese reflected a contempt for what they saw as a barbaric race, based on experience during the war and other factors such as Japanese pre-war behaviour in China. Japanese behaviour against the Allies reflected a contempt for what they saw as an inferior race.
The political or other doctrines governing a nation in war also seem to dictate the extent of observance of the rules. Japanese behaviour in WWII was entirely different to behaviour in the war against Russia only a generation before. The difference was the existence of the new militarism underpinning the militarists running Japan in WWII. Similarly, extreme German behaviour in WWII was entirely different to German behaviour in WWI, barely a generation before. The difference was the existence of Nazi ideology which in many respects parallelled Japanese militarist and racial supremacy notions.
The notion of the “laws of war” is a facade which we use to hide what we see as our inner barbarities.
That’s a fair but bleak view. The laws of war are an attempt to minimise the harm war does, and to try to contain barbarity. It’s no different to other laws in having good intentions but being unable to stop the behaviour it proscribes. Murder has been against every code of law everywhere forever, but nobody has managed to stop it yet. That’s not a reason for regarding it as a useless law, or a façade used to hide behind the individual barbarity that murders represent.
Current military training in all developed nations is very strong in law of war instruction. Whether it works in the heat of certain battles is a different issue.
I think it rarely breaks down in general unless one side is disposed to observe the rules and the other isn’t. The obvious example is Japan (which actually announced that it would observe the Geneva conventions at the start of the war) which resorted to practices wholly foreign to the Allies. An earlier example is the Boers in the Boer War, where the Boers did the same thing to the British, and produced the first example of concentration camps, run by the British in response to guerrilla tactics they couldn‘t meet effectively. This introduces the special problems for conventional forces facing guerrillas or irregulars. A current example is Iraq which, like Vietnam, has the problem that conventional military forces are subject to random attacks by guerrillas and irregulars against whom they usually cannot respond effectively, or often at all. When the enemy doesn’t play by the rules it induces an attitude that as the other side has thrown away the rule book, then so can we. Being the target of attacks without an identifiable enemy who uses hit and run tactics or tactics such as road bombings in Iraq, inevitably produces pent-up hostility towards those forces which can be expected to result in extreme responses on some occasions when the conventional forces are acting against what they regard as the enemy or its supporters. All this begs the question of whether there should in law be any rules applying to combatants who don’t observe the rules of conventional warfare but who expect to be, or at least who are, protected by laws of war. But that’s a wider topic.
We try to make our wars “humane”, but that is an oxymoron.
I couldn’t agree more.
It’s also absurd in the extreme.
Does it make any difference whether you get nuked, napalmed, phosphorous burned, or blast burned; or hit by a dum-dum or an M-16 round that is inherently unstable in flight and will tear a much bigger hole in you than a dum-dum under certain conditions?
But these quaint distinctions are no different than other paradoxical attempts to regulate violence and its consequences, e.g. rules in boxing. When Mike Tyson bit Evander Hollyfield’s ear off everyone was appalled. But if he’d stuck to belting him senseless over the next hour, and maybe rendering him a vegetable or even killing him in the process, it would have been alright and everyone would have thought it was a fine entertainment. Or amateur boxers wearing head protection but professionals not (possibly on the grounds that professionals have less brain to damage anyway )
If negotiations and diplomatic agreements were ever still an option, the parties involved wouldn’t be fighting a war.
True, but there’s the old line that war is the continuation of politics by other means.
It’s not unusual for modern wars, and warlike conflicts, to be resolved, or at least for the parties to try to resolve them, by diplomatic contacts during the conflict rather than on the battlefield. Even Japan was trying to end it’s war in WWII by diplomatic approaches to the Allies in 1945, albeit mostly and rather foolishly through Russia which had no interest in aiding that process. Of course, they are impelled to resort to diplomatic efforts only when the war isn’t going their way.
It’s hardly an original suggestion, but if the politicians and others who start wars and other international conflicts had to fight them themselves, and better still fight them out to the death between the politicians on each side before the real war could start, they’d be a lot less keen and we‘d all be better off.
Compare it with a bombing of Japane or Germany.