Kill all Warbands leaders.
Warbands are elemental-themed unique packs of monsters. They were originally introduced during the Warbands league but were not added to the core game when the league ended. Warbands are still available through other means, such as certain Delve nodes, and certain maps such as Iceberg Map, Lighthouse Map, Shipyard Map and Acid Caverns Map.
Warbands are separated into four tiers. The tier of a zone determines what kind of monsters can spawn. Tier 4 allows for the toughest warbands (the bosses) while tier 1 only spawns the weakest.
The current tier of the zone could be found with two methods:
| Tier | Restrictions |
|---|---|
| 1 | Level 2+ Zones (Zones may have two dots, but it doesn’t seem like Tier 2 units will spawn) |
| 2 | Level 10+ Zones |
| 3 | Level 41+ Zones (Cruel+) |
| 4 | Level 56+ Zones (Merciless) |
In addition to those restrictions, zone level will also affect the number of potential warbands can spawn from each tier. At lower levels you’ll only see 2 warbands, where as on 68+ zones up to 6 warbands can spawn in total. Chaos Renegades, the fourth Warband faction, are hostile to both other Warbands and to exiles. They can only spawn in tier 4 map areas.
The tier will be determined by the number of warband kills in a zone; every 10 minutes (60 minutes for maps) the zones with the most warband kills will have their warbands removed, while new warbands will appear elsewhere in world increasing the strength of warbands in adjacent zones. Warbands will follow the regular world layout, for maps they follow a layout similar to the map upgrade path (see the graph).