Sylvan is Jadame's old woodland confederacy: elves of the deep canopy, treant elders, the druidic circles that mediate between them, and the human ranger-clans who long ago took the forest's oaths. They are not isolationists by preference. They are isolationists because every century or so a foreign power decides the timber belt would make better farmland, and Sylvan ends that conversation in the trees.
The faction's magic is rooted, literally — the druids draw on a network of bound groves, each tied to a specific old growth that has been kept alive and lucid for generations. This makes Sylvan armies extraordinarily strong on familiar ground and merely competent off it. Their economy is similarly local: they do not mine, they harvest; they do not forge so much as grow and graft.
In Olden Era, Sylvan is contending with two new pressures. The Hive's southward expansion is chewing into the forest's underlayer in a way no previous invader has, eating not only the canopy but the mycelial network the druids depend on. And the Temple's expansion northward — peaceful in intent, the Temple insists — has begun to convert border villages whose people once paid forest-tithes. The druids are not yet at war with either, but the circles are arguing about when.
For players, Sylvan is a tempo faction. Fast units, strong ranged, and a magic school that turns terrain into a weapon. The trade-off is fragility: a Sylvan stack that gets caught in the open by Temple cavalry or Dungeon shadow-magic will not have a comfortable afternoon.