Regiments can earn experience to reach higher ranks and improve their attributes. Ranks are capped by your Warlord Level. Your regiments can earn experience in multiple ways.
At the end of every battle all regiments that participated in the fight will gain experience. The experience earned this way is equally shared across all regiments, so the amount of experience per regiment will increase if you fight with fewer regiments. For example, for a battlefield designed for 5 regiments, you can choose to deploy only 4 or less, so selected regiments can get more experience for this fight.
Battle experience can be earned by liberating Shires, fighting PvP Battles, stopping the Riding Brigands (Loot Wagon battle), raiding Strongholds, invading Brigand Island, and challenging Bosses.
Potions are one of the rewards you can earn from winning Battles, expeditions in the Sky Arch, and opening Chests from Ships. You can also purchase Potions from the Merchant or at War Harbor.
There are the four different Potions of Knowledge you can obtain in the game:
3. Sky Arch
You can send selected regiment(s) on an expedition to earn experience and find rewards on their quest.
The amount of experience gained in the Sky Arch increases with your Warlord Level and with the duration of selected expedition. The longer the expedition will take, the more experience your regiments will gain. An expedition lasting 16 hours will grant them the highest amount, however if you would send them on two separate 8 hour expeditions, they would earn more experience in total. The highest amount of experience when compared directly, your troops will earn when being sent on 8 separate 2 hour expeditions.
When a regiment has reached Rank 23, they won't be able to accumulate more experience.
There is another type of experience you can acquire, Warlord XP that will improve your Warlord Level. Warlord XP is gained when applying upgrades to your regiments.