American Dad! (2005)

S3E9 The Best Christmas Story Never Told

An injunction stops Langley Falls from lighting their beloved Christmas tree, and Stan points fingers at secular non-believers for ruining his cherished holiday. With his festive mood at rock bottom, the Ghost of Christmas Past appears to help him rediscover the essence of Christmas. Yet, Stan believes that the holiday can be salvaged by altering the outcome of the Vietnam War. Unfortunately, he soon learns that meddling with the past leads to unexpected and drastic changes in the future.