Why did demobilization after world war i lead to a temporary economic downturn?

Someone told me that war was fixed because it is used to bring down the population and so the government does not have to pay the pension of the killed solders. Because why did they not killed Hitler sooner and why did they not give the solders protection on D-day. So it is all the governments fault. and what will happen after this recession.

imma have to go   the third option

sorry if i am wrong hope this

if i am right plz give me brainliest