I think you would need to think in the line of a global economy/technology/infrastructure collapse (no power production/utilities, (global) transport, financial

I think you would need to think in the line of a global economy/technology/infrastructure collapse (no power production/utilities, (global) transport, financial crisis), millions of first world being thrown into third world conditions (no access to water, food, medicine) due to the large cities depending on technology. Also see: https://archive.org/details/james-burke-connections_s01e01 https://archive.org/details/james-burke-connections_s01e01