Ideas for Zethul - Druids

I was letting my mind wander last night and brainstorming ideas for Zethul, my homebrew campaign, and I thought about an interesting idea involving the priest spellcasting classes. In most campaigns I've played in, the Cleric and Druid classes are either allies in the same cause or neutral -or indifferent- to each other. What would happen if they were outright hostile?

As I've mentioned here before, Zethul is a kingdom where the churches are by decree outside the city proper, with their offices and places of worship situated along an avenue of sorts outside the main wall, but within an outer wall. These two concentric circles are the first and foremost defense to outsiders.

As in some modern cases, I picture that these more organized religions might wrongly disdain and dislike 'paganistic' deities and nature spirits, thinking them crude or evil. For this reason, Druids and their followers practice their beliefs in secret and seclusion to avoid outright persecution.