There was no Nethicite to war over before the Occuria gave it to Raithwall to end the war. It's all locked away far beyond any normal person's ability to get it. And after Raithwall ended the wars that plagued the land, there was a golden age of peace and propserity.

You're right Vayne started the war in FFXII to steal Nethicite but that's on him and his co-conspirators Venat and Cid, not the Occuria.