The game can be won by closing all four labyrinths before the horde over runs the map
While battling the horde and delving in to labyrinths, you want to be careful not to trigger any lose conditions. As members of the horde spread throughout the map, they corrupt and overrun the lands. Each enemy has a corruption level they contribute to the area they are at. If a location ever hits the corruption threshold it is considered corrupted. Corrupted lands cause the spread of the minions of the horde to happen to adjacent lands much quicker. If you have too many locations corrupted (based on the size of the map) the lands become overrun and you lose.
Enemies at your basecamp is especially dangerous. If your basecamp ever has enough enemies inside it to cause the location to be corrupted, then your basecamp is destroyed and you lose the game.
You also want to make sure the lands have enough safe areas. A location is considered safe if there are no enemies there. If you have too few safe locations (number based on map size), then you are overwhelmed by the forces and lose the game.
If any player ever ends the round with a wound in all three of their ability slots, then their character perishes and the game is lost.