Refers to damage or harm caused by war, including physical destruction, casualties, and economic loss.
その国は戦争被害から復興するのに何年もかかった。
It took many years for that country to recover from the war damage.
戦争被害 is a plain, neutral term for damage caused by war, while 戦禍 is a more emotionally charged, literary word for the same thing.
Compound of 戦争 (sensō, 'war') and 被害 (higai, 'damage').