

It's almost certain that the Skaven at Clan Rictus will also harass you. Beastmen and savage orc hordes are going to plague your attempt to keep and hold your heathlands. The heathlands you take are extremely vulnerable to being re-taken, even by relatively low strength opponents.

Only your main magic forest has defenses of any significance. However, the greatest challenge of the very early game will be dealing with beastmen and savage orc hordes. You start out the campaign at war with the Dark Elf faction, Bleak Holds.

These adjacent provinces are called "heathlands" and control over these provinces is key to upgrading the health of your magical forests (and ultimately the Oak of Ages too.) Note that control can be either personal control, or control by an ally (which includes both defensive alliances and military alliances.) As a Woodelf faction, your overall goal is to secure the provinces that surround your magical forest.
