What event killed 50 million–100 million people worldwide after world war i?

The Spanish flu pandemic of 1918

Hey there! :D

The event that killed 50 million- 100 million people were the 1918 Flu Pandemic. It killed millions of people and is said to be more deadly than WW1 itself. 

It actually affected around 500 million people, influencing the economy, workforce, and overall stabilization of countries and cultures. 

I hope this helps!
~kaikers