It's all Luther's fault!

So it's basically all Luther's fault that we mix Santa in with the birth of Christ.

In the Netherlands and many other European countries, people celebrate "Santa Claus Day" (Sinterklaas, St. Nicholas) on the evening of December 5th, when they exchange gifts and the children celebrate (Santa) who brings them their presents.  In these same countries, the "religious" people also celebrate December 25th as a separate and strictly "Religious Holiday" for church service and a meal.  In other words, they don't mix the two together.

During the reformation, Luther decided he didn't like celebrating a Roman Catholic tradition (St. Nicholas Day) and he wanted to wean German children off of St. Nick, so he created Krist Kindle, the winged Christ cherub, who also flew and brought gifts to good children and incorporated that fantasy into the celebration of the birth of Christ which was Christmas Eve.

Therefore, since America was established by protestants, they did not establish a December 5th celebration for "St. Nick".  As more and more Europeans' immigrated to this country, their celebration of Santa got joined to what we know as Christmas.

Thanks a lot Luther!  If you had just left it alone, we would be celebrating December 25th as day focused exclusively on Christ and letting those who wanted to lie to their children about a Saint who still flies around and delivers gifts to "good" children have their own "Santa" day on December 5th.