Great Frisian War participant Van Heeckeren
Background
The immediate cause of the war was a feud between the East Frisian tom Brok and Abdena families that got out of hand. Underlying reasons can be found in the civil struggles that existed throughout Frisia during the 14th and 15th centuries, having escalated from constant disputes in which one side would react with increasing hostility to the actions of the other. In these struggles, feuding parties would seek alignment with other opponents of their enemies and in doing so weaved an intricate web of alliances and loyalties. What also played a role in many disputes were the interests of the Frisian chieftains, who either strove to increase their power or to maintain the status quo.
In the Great Frisian War two parties opposed each other, composed of different groups from all over Frisia. One side was made up by the Skieringers (Dutch: Schieringers) in Middle Frisia, the van Heeckeren family in the city of Groningen, opponents of the Onsta family in the Ommelanden, and the Abdena family of Hisko Abdena in East Frisia. The other side, who together formed the Allies, were the Fetkeapers (Dutch: Vetkopers) in Middle Friesland, the van Bronckhorst and Onsta families in modern-day Groningen, and the tom Brok family of Keno II tom Brok in East Frisia.