I have a city on the edge of the sea and an ancient forest. The forest was protected for generations by local rulers but current ruler get bribed by foreign guilds to allow logging. The trees are old and huge and the water for transport is near so the guilds are reaping huge profits allowing to continuously sponsor the ruler.
There are some "forest people" that oppose the logging but I want the city people to join the struggle and I wonder what could motivate them to take up arms in such conflict and then protect the forest later if they win?
The city people are supporting themselves most from the sea and the trade so there is not much financial incentive to fight. I would say that some would have incentive to continue logging for profit if foreign guilds monopoly would be broken.
The local ruler is passive do not have much enforcers of his own and is a vassal subordinate to higher level lord. His superior would wholeheartedly opposed to logging but have his own bigger problems and cannot afford any internal struggle at the moment. So if the guilds can be kicked out quietly then nobody would make a fuss.
The forest is considered the most beautiful in a continent and to some extent considered a cultural treasure but I think such sentiment would speak more to aristocracy and not to common people who I want to risk their lives and who do not get much direct benefit from it themselves.
The city people do not have to come up with the impulse by themselves, there some outside forces that try to rouse them but they have to have convincing argument.
The social and technology level corresponds to medieval/renaissance.
Clarifications The city people follow religion which emphasizes order and hard work, in the forest there is a sect spreading that focuses on self sufficiency and living in harmony in nature but it is foreign religion and have only handful of adherents. The local religion is well entrenched so I think making population switch is the same question - it needs some strong impulse to happens.
The woodcutters are foreigners, have similar culture and follow different branch of local religion. There are a lot of them about 2000 for a city population of 5000 (and most of woodcutters are young and strong whereas city population includes children, old and infirm).
The city "merchant" elites have reasons to oppose the logging guild but are week and few and bulk of city population is made from poor warehouse workers, sailors and fishermen.
Disclaimer: This is a scenario for a RPG but I feel it fits wordbuilding SE much better.