Founded by Twin kings ages past, the Twin kingdoms of Thyan and Salatra have warred for centuries. Never in these wars has one side prevailed, and a strong sense of honor governs their warring.
Other kingdoms which have sought to take advantage of this perpetual discord have found, to their dismay, that they instead face the combined wrath of the two kingdoms, equipped with the best trained warriors the world has known.
Geography
Through fate and successful campaigning, each kingdom includes much productive lands - mineral rich hills, fertile farmland and game-laden forests. Between the two kingdoms is a vast expanse of farmland with few natural barriers. It is this lack of a natural break which leads to the perpetual battle between the kingdoms.
Politics
Each kingdom is a classic medieval society shaped by feudalism. The royal families of the two are closely related and intermarriage between the two is common, even with active warring between the two. Some pairing have actually resulted from battlefield encounters.
War
Battles are still bloody, but extensive use of Ransoms has led to less death then one would expect. With that, and the disuse of peasant levies or other light troops allows for wars to be fought for extended periods without crippling either nation financially.