1389 conclave
The 1389 conclave was convoked after the death of Pope Urban VI. The conclave is historically unique because all of the cardinal electors were the creation of a single pontiff: Urban VI, the very pope who was being replaced. None of the surviving cardinals created by previous popes recognized Urban VI as legitimate. In addition, Urban VI had deposed four of his creatures, and three were absent, leaving only sixteen cardinal electors.