What is the cause of the feud between the families of Ulrich Von Gladwitz and Georg Znaeym?

The feud between the families was caused by a dispute over a piece of land.

The forest lands of Gradwitz were of wide extent and well stocked with game; the narrow strip of precipitous woodland that lay on its outskirt was not remarkable for the game it harboured or the shooting it afforded, but it was the most jealously guarded of all its owner's territorial possessions. A famous law suit, in the days of his grandfather, had wrested it from the illegal possession of a neighbouring family of petty landowners; the dispossessed party had never acquiesced in the judgment of the Courts, and a long series of poaching affrays and similar scandals had embittered the relationships between the families for three generations.