What happened was that after the end of WW1, Greece occupied a large chunk of the former Ottoman Empire. Not content with the Greek populated areas around the eastern Aegean, the Greek army marched into central Turkey in order enlarge the area they controlled. This was driven by internal Greek politics. The Greek offensive was met by the new nationalist Turkish army of Kemal Ataturk. Ataturk was in the process of forming a Turkish state upon the wreckage of the former Ottoman Empire. A state based on Turkish nationalism, secular, and free from the bonds of Islam. The armies met in battle and the Greek army was routed. Ataturk’s forces pushed the Greek army clear out of western Turkey. Unfortunately the Greek minority population of the area was pushed out with the Greek army. The Western powers saw in Ataturk a strong bullwark against Bolshevik infuence in the Middle East, thus they did not back up Greece. The ultimate blame for these events rest in Athens, as the Greek governments need to prove themselves led to this disaster.
A quite reasonable summary of events.
All sides committed horrible atrocities.