War of Humans and Demons

The war which happened between humans and demons over 200 years ago.

Cause
Demon Kings followed demon tribes, and demon tribes followed demon king and they have often invaded each other. At times, it has developed into a major war that has taken the world by storm.

Results
Because of the war, human civilization hasn't developed very well. But some technologies improved.
 * Military Power: Military power, which is essential for war, expands the more wars are fought repeatedly.
 * Mobility: Transporting soldiers is an important aspect of war. Sturdier and faster horse-drawn wagons are being developed.
 * Expansion of Supply Lines: Supporting supply lines is the first consideration in military operations. Various efforts and innovations are being made for this purpose.

There are even stories of tools being developed to dig waterways more conveniently and comfortably by applying weapons developed for war.