The tradition has its roots in religion, of course, but also in immigration patterns. At the beginning of the 20th century, Jewish people were one of the largest non-Christian immigrant groups in the United States, as were Chinese people. That meant there were new populations that, by and large, didn’t see December 25th as a holiday. While most other shops and restaurants in U.S. cities closed their doors for a day, many Jewish and Chinese immigrants found something of a shared experience. – CityLab