UK History: Chapter 6, Exercise 1 — Possible Solution
======================================================================

THE THREE CAUSES
1. Edward III's creation of powerful duchies for his sons.
2. Bastard feudalism: magnates keeping private military retinues.
3. Henry VI's mental instability, which revived Richard of York's interest in
   claiming the throne.

LEAST FULLY DESCRIBED
Bastard feudalism: the source names it without defining it, and I did not
research it.