Once you have declared your intent to Pillage that province, the other players have a chance to join the battle.
Starting with the player to your left and going around in clockwise order, each player (including you) may, if they wish, move one of their figures from an adjacent province into an empty village in the province you are pillaging. Moving a figure in this way does not cost Rage, and even players with zero Rage can do it. (Note that Ships cannot be moved.) The option to move more figures into the battle goes round and round the table, and even if you first pass, you may still do it later on. Once all villages in that province are occupied, or when no one else wishes to join in, the battle begins.
Note: There are no villages in Yggdrasil, so any number of figures can join a battle there.
If at this point there are no enemy figures in the province or its supporting fjord, no battle takes place and you automatically Pillage the province, gaining its reward and flipping its Pillage token to its “pillaged” side. Note that in this case you don’t gain any Glory for winning battles.
Otherwise, a battle will take place, and all figures in the province being pillaged, or its supporting fjord, must participate in it.