And when they drew near to Jerusalem and came to Bethphage, to the Mount of Olives, then Jesus sent two disciples, saying to them, "Go into the village opposite you, and immediately you will find an ass tied, and a colt with her; untie them and bring them to me. If any one says anything to you, you shall say, 'The Lord has need of them,' and he will send them immediately." This took place to fulfil what was spoken by the prophet, saying,
"Tell the daughter of Zion,
Behold, your king is coming to you,
humble, and mounted on an ass,
and on a colt, the foal of an ass."
The disciples went and did as Jesus had directed them; they brought the ass and the colt, and put their garments on them, and he sat thereon. Most of the crowd spread their garments on the road, and others cut branches from the trees and spread them on the road. And the crowds that went before him and that followed him shouted, "Hosanna to the Son of David! Blessed is he who comes in the name of the Lord! Hosanna in the highest!" And when he entered Jerusalem, all the city was stirred, saying, "Who is this?" And the crowds said, "This is the prophet Jesus from Nazareth of Galilee." Matthew 21:1–11 (RSV)
In 1925, Pope Pius XI declared the last Sunday of Pentecost would be Christ the King Sunday. Fascism was rising in Italy and Germany, which centered on the cult of Der Führer or Il Duce. The modern trend of reducing the Christian faith to a private affair was gaining traction. In the aftermath of WWI, there was a rise in godlessness due to the war's carnage. Pius XI established Christ the King as a witness that Jesus is still the Lord and King of all things.
Sadly, WWI was followed by WWII, then Korea, then Viet Nam, then a variety of wars in the Middle East as well as small wars around the world. Godlessness continued its increase, first in Europe, then spread to North America and beyond. Even today, various political groups are vying for power throughout the world. As Ecclesiastes notes: 'there is nothing new under the sun.'
We can say 'thank you' to Pius XI for reminding the Church that despite all the wars, petty tyrants, godless lives, and other follies of the human race, that Jesus Christ is our Lord and King. He rules overall, and this fallen world will one day be made new.