The feast of Christ the King is one of the most datable in the calendar: Pope Pius XI instituted it in 1925 in the encyclical Quas Primas. Its context was explicit. Written in the aftermath of the First World War and amid the rise of secular nationalism and totalitarian movements in Europe, it asserted the kingship of Christ over states and societies as well as souls, a deliberate counter-claim against ideologies that made the nation or the party ultimate.
Pius set it on the last Sunday of October, before All Saints. In the 1969 revision of the Roman calendar it was renamed the solemnity of Our Lord Jesus Christ, King of the Universe, and moved to the last Sunday of the liturgical year, the week before Advent, so that the year now ends by proclaiming Christ's reign over all time before it begins again with his first coming. Several Protestant churches that follow the Revised Common Lectionary have adopted the day, often as "the Reign of Christ", giving a twentieth-century Catholic feast a modest ecumenical afterlife.