Question

How is this a negative thing related to war and economics.

most wars create zones of intense destruction of capital such as farms, factories, and cities. These effects severely depress economic output. ( I understand that bombs and other wartime activities wreck things but how would economics be involved)

Answer 1

When factories are bombed, they are useless and can't produce goods -- therefore there's no money coming in. Cities need to be rebuilt -- especially their infrastucture of roads, water supplies, and sewage removal. That costs a lot of money to repair these utilities. When farms are destroyed, the crops are ruined, so the people have to spend more money to buy their food from other places.