Complex sentence: The resort celebrated the 50th anniversary of Disneyland Park from 2005 to 2006 in an 18-month celebration known as the Happiest Homecoming on Earth, part of the larger Happiest Celebration on Earth promotion at all Disney theme parks.
Split into simpler sentences: The Resort celebrated the 50th anniversary of Disneyland Park from 2005 to 2006 in an 18-month celebration known as the Happiest Homecoming on Earth. This was part of the larger Happiest Celebration on Earth promotion at all Disney theme parks.