Complex sentence: In 1994 Carey released her first holiday album "Merry Christmas", which has become the best-selling US Christmas album of all time, and has produced the worldwide classic "All I Want for Christmas Is You".
Split into simpler sentences: In 1994 Carey released her first holiday album, "Merry Christmas", which became the best-selling US Christmas album of all time. It contains the worldwide Christmas classic "All I Want for Christmas Is You".