The play can roam the world and capture outposts.

Outpost can be reinforced

A Fortress protects the outpost. It stores gathered resources and maybe expensive production facilities. A fortress contains a Spawn Crystal, that can spawn minions to protect the fortress. (todo: rename spawn crystal to something more ingame)

Spawn crystal has an amount of energy, which is consumed by spawning minions and other tasks it performs. The crystal also supports the creatures existing on the battlefield.

The attacker also brings a spawn crystal, which performs the same functionality. When one of the crystal runs out of energy, the battle is over. This will not happen in the common way 'YOU LOST'. The run-out crystal will simply stop spawning and providing energy to the combatants, causing them to loose power (and die in case of minions). This way the battle is lost in a more gameplay-featured way. It also allows for features like retreating.

The Players fighting in the battle will also drain from the energy of the crystal. This way it might be possible to fight wars with different player setup:

• Battle of 2 players capturing an empty fortress. The fortress' crystal will spawn more minions then the attacking crystal, which should cause a balance in the battle
• When in 1v1 or 2v2, minion count will be equal, but 1v1 will have more than 2v2

This system implies that Players can't cast spells from their own energy. The Fortress Battle has to be a closed system:

All possible skills must be predictable at the start of the battle. This points to a combat system where the environment is used for spellcasting. Players could carry those energy crystals to draw power from, but entering a fortress battle should somehow disable all damage or power increasing effects there might be in a game.

The Combat moves learned by the Players or self-created moves, are considered predictable. It is part of the gameplay to know what moves exist, much like knowing what openings exist in RTS.