I did a lot of research for Nightmare Enemy, Dream Friend, and one area I had to familiarize myself with was how Germans celebrated holidays and which holidays were celebrated. Since the book centers around a Christian nation succumbing to an un-Christian ideology, I had to know all the major Lutheran and Christian holidays and how they were practiced at the beginning of the 20th century. I remembered that the Christmas tree tradition arose in Germany and has been transferred to the rest of the world, but I didn’t know exactly how Germans decorated their trees. During my research on several websites, I learned about the advent wreath—an even older tradition, variations of which are found in most northern European countries from Ireland to Finland. I also learned what Germans ate on Christmas: carp and potato salad. Later I had to do similar research for Welsh Christmas celebrations and was enchanted by the Welsh tradition of communal singing and the use of red dragons as Christmas decorations.
Because I am a history buff who enjoys reading history and biography, doing the research was not a drudge, for I genuinely enjoy learning such details that help bring the narrative to life. Besides, I always learned other things that I did not use in the novel. For instance, how did the Christmas tree tradition get transferred to the rest of the world?
The answer is fascinating, for the route went through the upper classes in Europe, but through the middle and lower classes in America. During the 1800s, German royalty intermarried with royalty from other countries in Europe; the most famous marriages were between England’s Queen Victoria and Prince Albert from Germany, and Russian Czar Nicholas II (himself descended from German and Danish nobility) and his noble German wife Alexandra. While that was happening, middle- and lower-class Germans were immigrating in droves to the United States; they were looking for peace from all the wars in Europe (some 50 wars and revolutions from 1800-1840), freedom, and prosperity.
Since England, Germany and Russia were monarchies, when the royal families of those countries began setting up Christmas trees, first the nobility, and then average people began to follow suit. Russia and England had huge empires, but Germany had a much smaller empire. The Kaiser was jealous of his grander imperial cousins, so one could say that World War One was due to imperial sibling rivalry.
In the United States, the German immigrants celebrated Christmas with trees, and, although this new idea was at first outlawed in some states, the obvious beauty of such celebrations could not be denied, so by World War One, most Americans had adopted the Christmas tree tradition. History.com has a more detailed explanation of the Christmas tree transfer.