An expansion is a base that was constructed by a player close to a gold mine in order to harvest gold. Expansions may only consist of the necessary buildings to mine gold, but often times also feature defensive buildings to help the player defend the expansion.
Due to militia-creeping and the human's power build expanding is very fast, easy and safe for humans. Because of this humans tend to expand very early on rely mainly on towers as defence. Humans usually have the most protected and biggest expansions, which often times also feature production buildings.
Building Great Halls takes longer than any other expansion. They are very vulnerable while being constructed, so orc players try to prevent the opponents from attacking their expansions in construction. They either try to hide the expansion from the enemy or force the enemy to another place by attacking their main base for example. On tier 3 orcs have access to the item Tiny Great Hall, which can be used to build an Great hall within only 20 seconds making it the fastest and safest way to expand. Orc expansions usually also have an Orc Burrow to be able to protect the mining Peons and a shop.
In contrast to other races undeads do not need to build their main building at an expansion in order to mine gold. Instead they must haunt the gold mine before they can mine from it. Still the Necropolis is necessary to teleport to the expansion to defend and and to reproduce fallen Acolytes. The undead expansion is considered the worst expansion because of several reasons:
- Vulnerability of Acolytes
- Blight is required, before defensive structures can be built
- Undead towers are the weakest towers, making it difficult to defend the expansion
Similar to humans and orcs, night elves also need their main building to mine gold. However the Tree of Life must entangle the gold mine before Wisps can mine gold. While Trees of Life also are vulnerable while being constructed, it is still much easier for night elves to expand than for undeads or orcs (with the exception of Tiny Great Hall). Wisps are usually spread out over the map as scouts and can be used to build expansions without having to move workers from the main base towards the gold mine. Additionally Trees of Life can be built before the creep spot has been cleared by building them further away from the creeps. When finished they can even help creeping the spot and root next to the gold mine. Night elf expansions usually only consist of the Tree of Life, as defensive buildings are not necessary, because the Wisps are protected by the entangled gold mine, while they are mining gold.