People in that town were divided into either enemies or allies, and fought against each other a long time ago.
この場合、次のような言い方ができますよ。
ーPeople in that town were divided into either enemies or allies, and fought against each other a long time ago.
「昔、その町の人たちは敵か味方に分かれ、互いに争った」
to be divided into「…に分かれる」
either enemies or allies「敵か味方かどちらか」
to fight against「…に敵対する・争う」
ご参考まで!