First of all, welcome to the forum :slight_smile:

There is a purge system, think of it like when you order a pizza to be delivered, you decide what pizza you want, a better pizza with more stuff on it requires more money.
It is sort of the same with the purge now.
First you have to place a treasure coffer and fill it with treasures or gold and silver coins/bars, the higher value your treasure has the higher level of purge you can order and have delivered to your base.
The purge does have some requirements that has to be met, they need a clear path to your coffer and a good amount of available sort of flat space close to your base for their camp, otherwise they refuse to come and attack you :grin: