But the date was obviously important to Christianity long before that and so other important events were held on the same day. Charlemagne was made Holy Roman Emperor on Christmas Day, 800 A.D. Pope Leo III designated him such as thanks for his support to the Church but he passed the crown on to his son without any ecclesiastical assistance and the Holy Roman Empire became a political/military organization rather than a religious one after his death.
And so the Roman Catholic Church survived any number of military leaders who asked how many divisions God actually personally provided for the Pope and in 1223, St, Francis of Assisi was around to create the first Nativity scene in Greccio, Italy.
Science isn't excluded from Christmas celebrations. In 1741 on Christmas day, Anders Celcius introduced the Centigrade temperature scale.
The western hemisphere isn't totally left out either, even if we came late to the party. On December 25th, 1492, Christopher Columbus and the Santa Maria docked at the Dominican Republic. On that same day in 1776, Washington crossed the Delaware and routed Europeans in New Jersey. Both involved alcohol.
Alcohol was also probably involved in the first Christmas celebration we can verify, that of 352 A.D., but definitely not the one in Massachusetts of 1652 when a fine of 5 shillings was assessed for "observing any such day as Christmas". Christmas got more popular once the Puritans calmed down and by 1831, Louisiana and Arkansas became the first U.S. states to make Christmas an official holiday. A year later Charles Darwin was on the Beagle voyage which would make him famous and celebrated Christmas in St Martin.
On Christmas Day, 1914, during World War I, an unofficial truce took place between the Brits and the Germans. Obviously the occupied French and Belgians were not all that eager for a truce but the Brits had a German monarch anyway, so it made sense. The German chocolate cake was supposedly delicious.
By 1939, the Christmas we know today - overt commercialism - was here, and Montgomery Ward introduced Rudolph the Red-Nosed Reindeer December 25th of that year.
In 1973, the first Internet crash occurred on Christmas day. An ARPANET programming bug caused all traffic to be routed through one university hub, Harvard, and it locked up the server. But they fixed it and on Christmas Day, 1990, the first successful trial run of the World Wide Web took place.
Yes, stuff happened between 1939 and 1973 too - but everyone already knew that Dick Tracy married Tess Truehart on Christmas Day, 1950 so I don't bother to mention it.