Before 1930 economics like lord Keynes followed say's which states that supply creates it own demand This means that people supplied commodities so a? to purchase others so every commodity is the market is a demand of another   There are all polices at that time were geared towards increasing income from the supply side. These policies however  could not work in Europe and other countries due to the economic depression that was pramiiity at that time

The economic depression was caused by the following

Over production which was not backed by an increase in aggregated demand

Most people did not have money and there was high level of unemployment

Low savings

Incomes low investment low invest rates etc and therefore   suoj.:y failed to create its own demand.

Money was issuer according to the gold standard i.e there was little money to purchase the commodities