On the "Old Calendar" (Julian calendar) this was December 25, so this was the date for Christmas, 1921.
This is actually considerably more complicated than it might seem, as the New Calendar is not the Gregorian Calendar used by the West and the Latin Rite of the Church, but rather the New Julian Calendar adopted in May 1923 by the Greek Orthodox Church. This caused a split over the calendar in the Orthodox Churches. The Russian Orthodox Church kept the Old Calendar, although by that time the Russian Orthodox Church was engaged in a struggle for its existence inside the Soviet Union, which was dedicated to its distinction. The civil government in Russia had adopted the Gregorian Calendar, used in the Western World, and now the whole world, on January 31, 1918.
Anyhow, in the Orthodox Churches, this was Christmas for 1921. With the largest Orthodox Church, the Russian Orthodox Church, under siege from the Communist government, and starvation rampant in Russia, it was not a happy one for the Orthodox.
The Dail approved the Anglo-Irish treaty, establishing the Irish Free State as a dominion. The vote was 64 to 57.
Dogsomyn Bodoo, Prime Minister of Mongolia, resigns after his efforts to make Mongolia into a Soviet style state meet with widespread opposition. He'd be arrested and executed the following August.
The Washington Naval Treaty agreed to ban the use of poison gas.
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This is also, I'd note, Orthodox Christmas for those Orthodox Churches that retain the Old Calendar today, and such Eastern Rite churches as may retain it.