Attack on Elector's State is a Dilemma event for The Empire and The Golden Order. The beginning will usually specify the attacking force, varying between Beastmen, Skaven, Greenskins, and Norscans. An example, is Beastmen Attack Elector's State! This will also specify a specific Elector Count and a settlement.
[Elector State} has come under attack from [Attacker] in the region of [random settlement owned by the faction] and are appealing to you for military assistance.
Will you come to their defence and join them in battle, or leave them to fight off their attackers alone?
Hire Nearby Mercenaries: You join the defence of [settlement], +1 Elector Count Fealty, -1000 Prestige
Send Scouts: -1 Fealty, gain visibility over region, -300 Prestige
Do Nothing: -1 Fealty
If you choose to join the defence, you start a battle with 5 or so spawned in units reinforcing the garrison of the settlement against the invading force. These battles are quite difficult as the friendly AI does little to synchronize with you and the attacking armies can be quite powerful. Effective use of Handgunners and Empire Knights are essential to victory. It also becomes much easier if the ally faction has an army garrisoned in the settlement, which makes it a more even fight.
There are no consequences to losing the battle, other than the settlement being occupied or razed by the attackers. +1 Fealty will be gained even if the battle is lost. If the settlement is close by as well, the player can reconquer it and give it back to the Elector Count for an additional +1 Fealty. The units spawned in for your faction are not retained either.
In general, it is best to fight the battles, as even losses will benefit the player. There is little point in sending scouts, unless your about to go to war with the faction or have no resources to send a force. Doing nothing also serves little purpose, unless the settlement is in your way somehow.