Sounds like the name of an anime doesn't it? The Sailor Wars are only really
mentioned in the anime. 
I'll
explain it the best I can, from what I know of the anime.
Many years ago a war broke out in space. Not one against countries, or cities. It was a war which placed Sailor Soldier against Sailor Soldier in an ultimate battle.
A force known as Chaos had been wrecking havoc in the universe for generations. Many soldiers fell trying to defeat the great force. All was not lost though, a legendary soldier rose from the shadows - the guardian of the galaxy, Sailor Galaxia.
Her great sword held tightly in her grasp, she plunged it into the heart of the ultimate evil. She felt that she was the only one who could defeat Chaos, that only she could control it. She did the only thing she knew to do and sealed Chaos deep inside of her, giving the galaxy a moment of peace. Soon though, the force of darkness started to overwhelm her, she knew she had made the wrong choice. She sent her light of hope away before being completely taken over.
Galaxia started her domination of the galaxy, pitting soldier against soldier in her quest for all the Star Seeds. The war started on one side of the galaxy until she came to Earth, where the final battle took place, the battle to end it all.
The Sailor Wars are never even mentioned in the manga.