Whilst you could probably argue that WW2 was started in Germany due to people voting "for the party which they think promises the most to the group with which they identify", it was the general population behaving that way, not only the elite - and it was the result of pretty extreme political turmoil and almost complete economic collapse. The kind of thing any country should be afraid of. (Those complaining about the bank bailouts should remember this).
The Allies didn't have much choice about entering WW2: they were either being invaded or seeing that in their near future. So I don't think it really fits with your imagined cycle of the elite causing "war, disease and destruction"
There were certainly social changes after WW2. I've never seen it suggested that they were due to "the elite having made their lives shit and need some help to get back on top again" though.
Women had entered the workplace whilst men were absent, and were still needed to rebuild the country. That's closer to the reason I gave: when there is competition for our work, we are valued and fairly paid. The learning to take from that is that to genuinely help people, we should train our young people and give them opportunities to become valuable, productive employees: not distort reward through an overly generous welfare state, so that an ever-smaller productive segment of the population pay everyone else to do nothing/do things which aren't useful. At the extreme, this was why communism resulted in such low standards of living - and we see that playing out in a bloated state here in the UK too.
There was also genuine optimism for the future from the whole population: including the political elite. I really don't think that the creation of the NHS, the welfare state, the UN etc came from any kind of attempt by the elite "to get back on top again". Again, I've never seen that suggested.
The political elite - it's true - were determined to take any steps possible to avoid going through the hell of war again - hence the de-natzification of Germany and the creation of the UN - but I've seen nothing to suggest it was because the war was their doing: just because it was hell.
Unfortunately, large institutions take on a life and direction of their own, when those in charge of them over-reach through a combination of belief in the importance of their own institution (which is partly knowledge and a sense of ownership, and partly hubris), and also because institutional growth and over-reach benefits their personal ambition. That's why the state (and international equivalents) have got bigger and bigger over the decades - to the point of the population's detriment, imo.