Is it possible to have one or multiple battles to continue for a decade or more in a fantasy medieval setting? The primary outcome required from the war is to have a constant stream of refugees.
The story takes place on a continent roughly the size of Europe with ocean on three sides and non-inhabited frozen mountainous regions to the north and north-east. Politically, most of the populated region is ruled by a single empire through methods of taxing and trade route control. There are many countries under the empire. The total population is around 70 million.
The magic system:
Almost all magic is internal to life, i.e. only a living being can perform and practice magic. All humans have the ability to perform magic. It is so common that many of the day-to-day activities involve using it, like making fire or fireless illumination, etc. Magic can be used to generate force fields (more like solidifying air into any shape for as long as mana is provided) which are used as weapons for both attack and defense). Magic in humans is very low in itself, and requires specific types of gemstones, which are specialized to enhance magical affinity. These gems are mined, and high quality gems are very valuable. With concentration and practice people can master their control over magic and with the right type of gem and excel at it.
While humans have the ability to use magic, they enslave a sub-human species who has no magic. These are fox people (no idea if there's a word for it): they are a head shorter than humans, have fox ears (and no human ears), and a fox tail. They are agile on their feet, and can hunt small animals by hand. They have to do most of the manual labor (farming, mining, transportation). Commonly this species is considered scum by humans, thus humans using magic in day-to-day work are seen as being blessed. Most of the refugees are to be their slaves.
The war is supposed to be between countries individually at first but, as time goes on, they form alliances and the fights get bigger. This needs to go on for at least a decade. Is this workable in the current setting?
The slaves do not provide any advantage in the war and are pretty useless as cannon fodder. The slaves of captured provinces are considered a liability and thus banished from the land. With nowhere to go and rejected by all, they move to the uninhibited north where without a master they start a new life of freedom.
Few point I missed
- The slave trade is the largest trade before the war.
- Most of the major capital cities have castle or citadel so majority of the war is sieges. And while doing so major part of the local workforce is striped.
- As slave have value they are not harmed in any manner but given a choice to move to the North area where they can survive on their own (with whatever skill they have). This is so that after war they can be recaptured and sold. (The attacking countries are northern close to the uninhabited north)
- The things they did not anticipate: The war last for 10 years and the rise fox people who fought back after the war.