What is your thesis that WW2 was the main factor in the demise of Empires.
It was WW1 that was the fulcrum that ensured the independence of the colonies.
Basically it was India that started the break up of the Empires. There is debate as to whether it would have occurred sooner or later without WW2.
Ghandi agreed to suspend the move towards independence for the duration of the war. But it was finance that in the end decided its freedom from Britain. This was inevitable, once the movement for freedom got under way, there was no way Westminster would have fought to keep it.
If you have doubts on this score go back to the English Civil war, Parliament is responsible for financing wars. The one against the Nazis and Japan was forced upon us.
Well someone had to stick up for the little man. Lets assume WW2 didn't happen.
Even if the political feeling had gone against independence for a period of time by the mid Fifties at the latest India would have gained its freedom, the head of steam was already under way in the 20s.
Remember basically English politics is at heart pragmatic. Once it was costing more than 10,000 civil servants (yes note this India was run by 10,000 civil servants) and a few local militia, India was not worth hanging on to.
It was gained from the French to protect trade, always remember this.
Once India had its freedom from Westminster others would demanded theirs.
Whether this was a good thing (in Africa especially) is a debatable point. Would Westminster have hung on to other colonies longer (especially in Africa) yes some weren't ready to run themselves, but would England have given them their independence at some point. Yes it is our reason for being here. Our point was to trade, it is these left wing socialists who say we shouldn't be in Africa that do the most harm to the indigenous peoples. We went there to trade and put an infrastructure in place. If there is criticism it is we didn't educate enough.
Would other nations (France Portugal, Belgium, Spain, Holland) it is debatable. Holland would probably follow England's lead, for the rest you would have to ask them, I suspect not.
Portugal was forced out of Goa. If you visit India check out Bombay (that's Bombay, I got told off by the street stall holders for calling it the other name) then see what Goa is like.
You will see why only the British and Romans new how to run Empire.