What key lessons did the politicians and economists learn from the interwar economic experiences?

The economists and politicians learnt two key lessons from the inter-war economic experiences.
(i) First, an industrial society based on mass production cannot be sustained without mass consumption.
(ii) There was a need for high and stable income which depends on full employment of the people.
(iii) Since market alone could not guarantee full employment; government should intervene and take steps to minimise fluctuation of market forces.
(iv) The second lesson is that the global economy is inter-related.
(v) The goal of full employment could only be achieved if governments had power to control flow of goods, capital and labour.