党同伐异

dǎngtóng-fáyì

[defend those who being to one's own faction and attak those who don't; unite only with those of the same ideas and attack the others] 拉帮结派, 偏袒同党, 攻击异己

原指学术上的派别之间的斗争, 后泛指一切集团之间的斗争

党同伐异, 此姘彼丑。 --周邦彦《汴都赋》