Actually....there are indeed indications that the German population was brought close to unrest by the bombing on two occasions in 1943 - one obviously being in the immediate aftermath of GOMORRAH. These are recorded both by Albert Speer, and Goebbels in his diaries. You also had the later-war example of the "Edelweiss Pirates" and other areas of bombed German cities being out of government control and descending into chaos.
Unrest in London led to several instances of a very near breakdown in law and order; the famous one being when Winston visited the East End and declared for the cameras that "the East End could take it" - off-camera the locals told him firmly and loudly exactly HOW much more they were prepared to take!
And Churchill had to be ushered off the scene rapidly...
The second was the incident of the Police having to issue and draw firearms to keep Londoners out of the Underground system when the Blitz began - one of the major fears of the government being that the population would go into deep shelter and not come out again,
especially for the next day's work; this all got rather ugly at a couple of Underground stations, but thankfully the government rescinded the order rather than enforce it further, and the Underground was opened up for nightly shelter.
if anything it shows how resilient people are in general, hell it took two nuclear bombs before Japan surrendered.
Remembering of course that the Japanese
people had little or no - make that just no - say in the matter...
Did an international understanding ever come to pass or is the bombing of civilian populations something that most countries just agree to not do without it being on paper?
You seem to have a quite "romantic" view of war and how it was done; to put it simply, you do whatever is needed AND that you can do...right up to the very limit that any international agreements made in peacetime permit -
and THEN go over those limits if you can make a suitable case to anyone listening....or
willing to hold you to judgement. In a world full of Neutrals you want to trade with, you pay attention to THEIR sensitivities over international agreements and how the keeping or breaching of them might hint at how you'd treat
THEM!
Governments don't come to polite agreements - they come to agreements by back channels because
there's something one party wants, and that the other party can screw them for. But often they don't come to agreements in wartime simply because they want the ability/right to do something
further down the line open to them.
Example - the USSR wasn't a signatory to the Hague Conventions after November 1917...but on the outbreak of the Winter War Stalin came to a back-channel agreement with the Finns that they would observe SOME negotiated elements of the Conventions between them during the war...in the summer of 1941, Stalin made the same offer to the Germans after the start of BARBAROSSA
but this time Hitler refused, because he was certain of German victory and saw no reason at all to grant any favourable treatment to the prospective "defeated"...
They also come to unspoken agreements
in a "balance of terror" situation - like the British development and testing of weaponised Anthrax mid-war being communicated to the Nazis to checkmate their potential use of newly-developed of nerve agents....
But beyond particular circumsntaces like that - war is hell. You do what you need to do to win. You don't
not do something because it's unpalatable...see under Mers-el-Kebir.
Twenty years ago we had Johnny Cash, Bob Hope and Steve Jobs. Now we have no Cash, no Hope and no Jobs....
Lord, please keep Kevin Bacon alive...