Given the task definition and input, reply with output. This task is about creating an unanswerable question based on a given passage. Construct a question that looks relevant to the given context but is unanswerable. Following are a few suggestions about how to create unanswerable questions:
(i) create questions which require satisfying a constraint that is not mentioned in the passage
(ii) create questions which require information beyond what is provided in the passage in order to answer
(iii) replace an existing entity, number, date mentioned in the passage with other entity, number, date and use it in the question
(iv) create a question which is answerable from the passage and then replace one or two words by their antonyms or insert/remove negation words to make it unanswerable.

Passage: When the Frankish rulers established the system of feudalism, the Bishops of Utrecht came to exercise worldly power as prince-bishops. The territory of the bishopric not only included the modern province of Utrecht (Nedersticht, 'lower Sticht'), but also extended to the northeast. The feudal conflict of the Middle Ages heavily affected Utrecht. The prince-bishopric was involved in almost continuous conflicts with the Counts of Holland and the Dukes of Guelders. The Veluwe region was seized by Guelders, but large areas in the modern province of Overijssel remained as the Oversticht.
What system ended the prince-bishops?