There was no Macroeconomics or Microeconomics 100 years ago: there was one Economics. Why did it split–what happened?
Microeconomics was first discipline to happen in economics. Micro means for each individual as a basis that suggests the consideration of subject as an individual , his behaviour and choices- preferences in an economy
Before 100 years on average we had economics focussed on the parameters and aspects at individual level but there are many endogenous as well as exogenous shocks in an economy that decides the choice set for an individual in an economy where collective choice and preferences of group of individuals matter which invokes thought of collective treatment of individuals assuming all individuals in an economy are rational and homogeneous. This actually called for another school of thought which gave rise to other equally important stream called as MacroEconomics. This newly born stream which actually coined by Sir Keynes grossly helped to solve or find solutions to intertemporal questions such as inflation, unemployment etc.
Hence it was need of an hour to segregate the streams of economics into two major parts Micro and Macro economics