A war that took on between
Zanarkand and
Bevelle, 1000 years ago from the events of FFX/
1002 years ago from the events of FFX-2. It was 100% assured that, from the start, Bevelle would've won.
The info on this war is quite...huge. Refer to Maechen in FFX, or to GameFAQs' FAQs and/or Message Boards.