In the Megila, it seems first that Jews have no specific enemies. But Haman is angry with Mordechai. Since he is angry with Mordechai, he decides the extermination of all Jews.
It seems that he knows how to play the chord. He uses old prejudices: Jews are not integrating into the nation. He has no problem convincing Achasverosh. It's known many people don't like Jews but there are not properly enemies.
Further in the Megila, we read that there was a war, Jews killed their enemies. The Megila makes it clear that there were known enemies. As if there was a kind of organized Nazi-like party, or another nation who was preparing for war against Jews.
At first reading it's obvious that the history is not clearly written. It's like there is a change of point of view in the narrative. How can we explain this?