The mine was giving a lot of magic crystals to the people of the village, however, they didn't know what consequences it could bring. There were creatures inside that should better be sleeping.
The zombies and skeletons that were sleeping in the mine for many years had awaken. The village will be destroyed if you won't protect it. Kill the creatures of the dark and place traps if you feel that you can't handle the amount of incoming attacks. Shoot with cannons, freeze the ground or place the saw fence to stop them at any cost!