Christmas carol lovers have a lot of people to thank for the carols we sing now. Most weren't written by Americans or within the last couple of centuries. The history of carols began a few thousand years ago in Europe as pagan songs sung while dancing. Every season was celebrated this way, with song and dance. Then early Christians, I’m talking VERY early, like 160-700 AD early, started writing songs for people with their religious beliefs. But because most of the songs were written in Latin, a language with Roman roots dating back to around 753 BCE, lots of folks didn’t understand the words, consequently, singing them passed by the wayside.
~ God Rest Ye Merry Gentlemen: unknown composer, English carol dating back to the 15th c.
~ O Come O Come Emmanuel: Gregorian chant 8th c; French text 12th c; translated by John M. Neale, English composer, 19th c.
Mr. Neale also wrote Good King Wenceslas and Good Christian Men, Rejoice. The latter comes from a 14th c German melody.
Singing carols in public became popular in large part because of groups called Waits. These were official carolers sanctioned by local officials to sing carols and collect money from the poor on Christmas Eve (AKA 'watchnight' or 'waitnight' because of the shepherds watching their sheep when the angels appeared to them). Singing in public gradually extended to singing carols during church services, as well as going door to door, and singing in the streets.
Thanks to these groups and the fact that around this time many orchestras and choirs began to emerge and people wanted Christmas songs to sing, carols once again became popular.
The Westminster Carol, better known in the US as Angels We Have Heard on High: This song has a history going back as far as 130 AD when people began chanting the phrase "Gloria in excelsis Deo" in Christmas eve worship services. Fast forward to medieval times when a Latin chorale version likely inspired the traditional French Christmas carol Les Anges dans nos Campagnes, which in the early 1900s, Edward Shippen Barnes from New Jersey, USA used to arrange the version we now know.
What Child Is This?: music from an Old English ballade, Greensleeves, text by William C Dix, 19th c.
Joy To The World: music by German composer, George F. Handel,(composer of The Messiah, 1714), text by Isaac Watts, 1719.