Mining is not a technically form of combat, but it is needed to support all other forms of combat. Miners wielding pickaxes chip away at deposits of resources, usually gold, to get the funds needed for an army. However, in a pinch, a pick could be used to deliver a modest amount of damage to an enemy unit.
The Way of Mining is simple and requires a pickaxe to obtain the resources and a bag to carry the resources back to a castle. All empires use the Way of Mining in some form except for tribals (which is why they died).
The pickaxe is swung at a deposit of resources to break off pieces of it to be carried and used. The pickaxe is not generally used as a weapon, but in worst-case scenarios, it can be used to deal small amounts of damage.
Miners generally bend over to reach the usually low-to-the-ground resources and swing their pickaxe at it. Mining is very simple which has led to its widespread use.
Order was a nation of miners, their native country had rich deposits of resources which Order mined to become a very rich nation. However, this made them a target for invasion and they were afraid that neighbouring nations such as the Archidons would invade for the resources. The club, being similar to a pickaxe, was researched and Order started The Conquering, where it invaded other nations so they couldn't invade Order.
Chaos required resources for their army too. Miners from the nations they conquered were enslaved and put in chains being forced to mine all day. It is unknown if Order freed these miners or slaughtered them after The Great Truce. However, it is likely that Order killed them to cripple Chaos.