I have long felt that Christmas has become an American Holiday more than a Christian holiday for many many years. I understand it is called CHRISTmas, but it has moved from just celebrating the birth of Jesus to a winter celebration in America, and probably most of the world.
There have been many celebrations in and around winter solstice. Hanukkah, The Saturnalia, Dies Natalis Solis Invicti, Brumalia, and Yule to name a few. The Winter Solstice is the mark when the earth's axial tilt is farthest away from the sun. It is suppose mark that the worst of winter is over. Most of the celebrations that occur at this time seem to be linked to fertility for the new year. Growing of crops, birth of cattle, etc. Feast were very common for Europe during this time, because livestock was slaughtered so they wouldn't have to be fed during winter because lack of grain. It was the only time of year that there was a large supply of fresh meat. Also most wine and beer made during the year was finally fermented and ready for drinking.
Christianity didn't celebrate Christmas till the fourth century. Till that time Easter was the main holiday for Christians. In the fourth century church officials decided to institute the birth of Jesus as a holiday. Pope Julius I chose December 25 because the bible doesn't mention the date for Jesus' birth. Many people believe Jesus was born in spring because shepherd wouldn't be herding in the middle of winter. It was thought that December 25 was chosen to make it easier to adopt the traditions of Saturnalia (A Roman holiday to honor Saturn the god of agriculture). By having Christmas at the same time as many other winter solstice festivals, church leaders increased the chances that Christmas would be embraced.
When the United States was Christmas was not a national holiday. Actually Congress was in session on December 25, 1789, which is the first Christmas under the U.S. Constitution (The Constitution was created September 17, 1787, but needed to be ratified by nine states to completed. New Hampshire was the ninth state to ratify the Constitution on June 21, 1788 after which Congress chose to start operations under the new Constitution on March 4, 1789). Christmas wasn't made an official holiday till June 26, 1870 (This fact should point out that the founding father were not Christian despite popular belief, but that is for another post).