The scorched earth mechanic can be done by the defending player in a war to slow down the enemy. This mechanic needs to cost money food and goods however so it cant be exploited. How it works is you pay to scorch earth your own province, the morale automatically goes to 25% and it wil automatically slow down any army (even your own army) that goes through it by (insert percentage). You automatically destroy any buildings that were built there if you use it though.