Complex sentence: Disneyland was dedicated at an "International Press Preview" event that was held on Sunday, July 17,1955, which was only open to invited guests and the media, although 28,000 people attended the event, only about half of those were actually invitees.
Split into simpler sentences: Disneyland was dedicated at an "International Press Preview" event that was held on Sunday, July 17,1955, which was only open to invited guests and the media. Although 28,000 people attended the event, only about half of those were actually invitees.